U.S. patent application number 15/611511 was filed with the patent office on 2017-12-07 for apparatus, method, and system for providing tunable circadian lighting at constant perceived brightness and color.
The applicant listed for this patent is Musco Corporation. Invention is credited to Samuel M. Berman, Bradley D. Schlesselman, Jason T. Schutz.
Application Number | 20170348506 15/611511 |
Document ID | / |
Family ID | 60479134 |
Filed Date | 2017-12-07 |
United States Patent
Application |
20170348506 |
Kind Code |
A1 |
Berman; Samuel M. ; et
al. |
December 7, 2017 |
APPARATUS, METHOD, AND SYSTEM FOR PROVIDING TUNABLE CIRCADIAN
LIGHTING AT CONSTANT PERCEIVED BRIGHTNESS AND COLOR
Abstract
The newly discovered retinal ganglion cell photoreceptor
melanopsin absent in the central fovea of the eye but distributed
throughout the remaining human retinal body provides both
non-visual biological/physiological input inducing circadian
entrainment, and visual input affecting perceived brightness; this
perceived brightness is not the object brightness commonly
associated with luminance and perceived color of an object in
central view, but the perception of brightness of a whole space or
task background. Discussed are improvements to circadian lighting
systems based on melanopsin stimulation whereby ambient and/or
device background lighting may be temporally tuned over a range of
prescribed color temperatures from a first subset of lighting
having a higher melanopic content to a second subset of lighting
having a lower melanopic content or vice versa in accordance with a
desired circadian cycle, and in a manner where net light output is
of a constant perceived brightness and color throughout temporal
tuning.
Inventors: |
Berman; Samuel M.; (San
Francisco, CA) ; Schlesselman; Bradley D.;
(Oskaloosa, IA) ; Schutz; Jason T.; (Oskaloosa,
IA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Musco Corporation |
Oskaloosa |
IA |
US |
|
|
Family ID: |
60479134 |
Appl. No.: |
15/611511 |
Filed: |
June 1, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62345559 |
Jun 3, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M 2021/0055 20130101;
H05B 47/16 20200101; A61M 21/00 20130101; H05B 47/19 20200101; A61M
2021/0083 20130101; A61N 5/0618 20130101; A61N 2005/0626 20130101;
H05B 45/20 20200101; A61M 2021/0044 20130101; Y02B 20/40 20130101;
A61N 2005/0628 20130101; H05B 45/10 20200101; A61N 2005/0651
20130101 |
International
Class: |
A61M 21/00 20060101
A61M021/00; H05B 33/08 20060101 H05B033/08; H05B 37/02 20060101
H05B037/02 |
Claims
1. A method of operating a spectrally tunable lighting system
capable of providing general purpose ambient or device background
lighting while simultaneously providing in unison temporally active
circadian stimulation lighting comprising: a. selecting desired
light levels based, at least in part, on the general purpose of the
lighting; b. selecting a range of circadian stimulation based, at
least in part, on desired ergonomic effects; c. selecting high
melanopic content (high circadian stimulation) sources or spectra
and low melanopic content (low circadian stimulation) sources or
spectra over a range of correlated color temperatures wherein: i.
the high melanopic content sources or spectra and the low melanopic
content sources or spectra are metamers coupled together by an
operating control profile such that the net perceived color and
brightness of the high and low melanopic content sources in
combination remains constant during transitioning cycles of
circadian stimulation.
2. The method of claim 1 wherein the sources are LEDs and the
operating control profile comprises varying input current or duty
cycle.
3. The method of claim 1 further comprising verifying melanopic
content of the sources with a light meter having an output modified
to incorporate melanopsin content (M/P values) using dimensionally
homogeneous M/P values based on equations 3 and 4.
4. The method of claim 1 wherein the operating profile is
determined, at least in part, on a user's preferred circadian
cycle.
5. An LED lighting fixture comprising: a. a housing; b. a first
subset of LEDs in said housing having a high melanopic content; c.
a second subset of LEDs in said housing having a low melanopic
content; d. electrical means to power said LEDs; and e. a
controller adapted to adjust the power to the first and second
subset of LEDs according to an operating profile wherein the
profile is determined, at least in part, on
physiological/biological benefits associated with the melanopic
content of the first and second subsets of LEDs.
6. The LED lighting fixture of claim 5 wherein the first subset of
LEDs having a high melanopic content are metamers of the second
subset of LEDs having a low melanopic content.
7. The LED lighting fixture of claim 5 wherein the electrical means
comprises one or more drivers adapted to operate the first and
second subset of LEDs independently.
8. The LED lighting fixture of claim 1 in combination with plural
lighting fixtures.
9. The LED lighting fixture of claim 8 installed at a target area
for illumination.
10. The LED lighting fixture of claim 9 where the target area
comprises: a. an interior of a building; b. an exterior space.
11. A method of illuminating an area comprising: a. selecting a set
of light sources comprising: i. a first subset configured to
provide higher melanopic content; and ii. a second subset
configured to provide lower melanopic content; b. selectively
driving the light sources between 0 and 100 percent intensity; c.
so that the set of light sources can be used for any of: i. general
lighting; or ii. circadian lighting.
12. The method of claim 11 wherein the general lighting comprises:
a. interior lighting; b. exterior lighting; c. general purpose
lighting, or d. background lighting.
13. The method of claim 11 wherein the higher melanopic content
comprises melanopic content effective to produce a sleepiness
response in melanopic receptors; and the lower melanopic content
comprises melanopic content effective to produce an alertness
response in melanopic receptors.
14. The method of claim 11 wherein the selective driving for
circadian lighting is according to a predefined profile, wherein:
a. the predefined profile transitions between higher and lower
melanopic content by the selectively driving of the first and
second subsets of light sources with: i. substantially
imperceptible shifts of perceived color metameric color output; and
ii. substantially constant spatial or background brightness.
15. The method of claim 14 wherein the transitions are based on at
least one of: a. predetermined time intervals; b. sensed
measurements; c. remotely controlled instructions.
16. The method of claim 11 wherein the first subset configured to
provide higher melanopic content has a relatively high percentage
of energy in the band around 488 nm, wherein on a scale normalized
to 1 said energy is at or above on the order of 0.20 between 478 to
498 nm.
17. The method of claim 16 wherein said energy is at or above on
the order of 0.30 between 483 to 493 nm.
18. The method of claim 17 wherein said energy is at or above on
the order of 0.40 between 486 to 490 nm.
19. The method of claim 11 wherein the higher and lower melanopic
content comprises a calculated M/P value related to SPD of the
light sources.
20. The method of claim 11 wherein the set of light sources is
embodied in a light fixture, luminaire, or module and further
wherein a plurality of said light fixtures, luminaires or modules
are aimed to provide illumination of at least a portion of the area
or space at the area.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C. 119
and/or 120 of and priority to U.S. Provisional Application Ser. No.
62/345,559, filed Jun. 3, 2016, which is incorporated by reference
in its entirety herein.
I. BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to adjusting
lighting source output to provide a biological/physiological
benefit to a user in accordance with desired circadian stimulation.
More specifically, the present invention relates to improvements in
so-called circadian lighting (also referred to as "bio lighting" or
"photobiology" or "light therapy") insomuch that shifts in
operational variables in the light source output which produce said
biological/physiological benefits--namely, dynamic shifts in the
melanopic content of the light which impacts, among other things,
alertness and also (i) do not result in a perceivably different
color of ambient or background light over the course of operation
and (ii) do not necessarily maintain a constant luminance or
illuminance but rather can maintain a constant perceived ambient or
background brightness.
[0003] Over the last few decades great effort has been spent trying
to understand what will be referred to herein as the human response
to lighting. A human response to lighting can be immediate and
physical--like squinting in the presence of a light source which
produces glare--or slower to evolve and more visceral--like a
diminishing effect due to seasonal affective disorder (SAD) over
prolonged exposure to appropriate light therapy. Research has led
to a widely accepted truth: lighting does more than just
illuminate, and the eyes do more than just see. More specifically,
lighting does more than facilitate vision--it has a
biological/physiological impact on the viewer.
[0004] To quantify circadian effects, a number approaches have been
taken. Melatonin, the active and causal hormone, has been measured
in subjects and correlated to circadian behavior which, in turn,
has been correlated to, among other conditions, alertness.
Experimenters have adjusted intensity and exposure to light in an
attempt to yield one or more biological/physiological benefits
(such as perceived or measured alertness); see, for example, U.S.
Pat. Nos. 8,028,706 and 8,506,612 both of which are incorporated by
reference herein in their entirety. Experimenters have adjusted
spectral power distribution (SPD) via selection of colored light
sources such as LEDs to encourage melatonin
production/metabolization or otherwise regulate circadian rhythms
(see again U.S. Pat. No. 8,506,612). Experimenters have even
adjusted the SPD of a light source comprised of multiple colored
LEDs by timed power or duty cycle adjustments to said LEDs in
accordance with anticipated circadian rhythms. These efforts can
produce a beneficial circadian lighting product, but they suffer
from a few deficiencies.
[0005] Commercially available circadian lighting systems produce a
"colder" bluish light during the day to initiate greater circadian
stimulation and a "warmer" reddish light during the evening, to
diminish said stimulation. The bluish light (i.e., the colder light
generally associated with higher correlated color temperatures
(CCTs)) is well known to be more effective at suppressing
melatonin. However, these commercially available lighting systems
are perceivably bluer during the day and perceivably redder in the
evening such that there is a prominent and noticeable color shift
and as well an overall perceived brightness shift during the
operation time. This is perhaps one of the reasons why many
commercially available circadian lighting systems are sold as
individual units such that they may be independently switched on
and off as needed to produce the desired biological/physiological
benefit, much like how one switches on a nightlight only in the
evening. The prominent color shift makes state-of-the-art circadian
lighting systems less suitable for general purpose lighting that
requires good color rendering for a task performed thereunder;
further it may be annoying or bothersome due to the visible color
shifting, especially for computer monitors and other personal
electronic devices where background lighting surrounding the visual
task is prominent. So, often times, any circadian lighting system
must either be paired with general lighting, or must be operated in
an "either/or" mode such that it is operated either as general
purpose lighting or in a special mode that provides
biological/physiological benefits (see again U.S. Pat. No.
8,506,612). This can be cumbersome and annoying as well as not
cost-effective for a user.
[0006] Some advancements have been made insomuch that under some
conditions the light produced in the "awake" (i.e., colder, bluer)
mode is much closer in perceivable color to the "sleep" (i.e.,
warmer, redder) mode (see U.S. Pat. No. 8,378,574 incorporated by
reference herein in its entirety) but the shift remains perceivable
even when the light is perceivably white and illuminance is
constant. Furthermore, when the illuminance is held constant the
perceived brightness of such illumination will be observed as
changing. This brightness phenomenon has been reported extensively
in lighting engineering literature and now attributed to responses
of the recently discovered melanopsin retinal photo receptor--such
having been found to be efficiently stimulated by bluer-rich
lighting.
[0007] The preceding poses a problem: state-of-the-art circadian
lighting systems rely upon adding blue light for an "awake" mode,
and transition to reducing blue and adding redder light for a
"sleep" mode; even systems employing "white" sources typically
include many RGB-type LEDs heavy in red or blue light. Therefore,
if one adjusts the SPD of the sources so to change the color
temperature of the light source (e.g., transitioning from colder
light to warmer light), even if one keeps illuminance constant, a
user will likely perceive a shift in color and brightness, wherein
the perceived shift in brightness is due to the response of
melanopsin receptors which are not accounted for in the calibration
of standard light meters. Therefore, using state-of-the-art
techniques it is not possible to produce a circadian lighting
system of perceivably constant brightness and color. Thus, there is
room for improvement in the art.
II. SUMMARY OF THE INVENTION
[0008] State-of-the-art circadian lighting systems produce
desirable biological or physiological effects when transitioning
from a colder bluish light to a warmer reddish light in accordance
with a desired circadian entrainment. However, these effects have
concomitant effects that are not considered desirable. Often, said
circadian lighting systems are not suitable for general purpose
lighting, since the perceived color of the lighting on the whole is
affected, as well as affecting specific tasks which require
assessment of color and so these must be supplemented with
additional lighting. Alternatively, said systems can be operated in
a general purpose task lighting mode, but not at the same time as
providing said biological/physiological effects, or if operated at
the same time they do not provide perceivably constant brightness.
In the former scenario, additional cost is incurred by the user,
and in the latter scenario adverse biological/physiological effects
(e.g., distraction from task) could be sustained as a result of the
changing perceived brightness.
[0009] Attempts have been made to incorporate circadian active
background lighting for electronic devices such as monitors,
tablets and cell phones. Desired circadian activity is presently
produced by varying the color and brightness of the device
background lighting but again is noticeably annoying and therefore
less desirable than the present invention.
[0010] It is therefore a principle object, feature, advantage, or
aspect of the present invention to improve over the state of the
art and/or address problems, issues, or deficiencies in the
art.
[0011] Technical research reports recently presented at the
national conference of the Illuminating Engineering Society
(November 2015) by Schlesselman, et al discussed findings relating
to concepts of brightness, melanopsin receptors, melanopic content
and widely known S/P (scotopic-to-photopic) ratios, etc. relevant
to the current invention. These reports are Schlesselman et al,
Brightness judgments in a simulated sports field correlate with the
S/P value of light sources (hereinafter individually"IES1" and
included later in this description); and Schlesselman et al,
Brightness matching determines the trade-off between S/P values and
illuminance level, (hereinafter individually "IES2" and included
later in this description) (hereinafter sometimes cited
collectively as simply "Schlesselman et al") which are included for
reference below in their entireties. In those reports the more
familiar S/P ratio was used as the highly correlated proxy for
relative melanopsin content (M/P value) of the viewed illumination.
Said research presented has demonstrated that it is not necessarily
the blue content or even correlated color temperature (CCT) of
light that triggers melanopsin receptors associated with non-visual
biological/physiological input with respect to circadian
entrainment, but rather the melanopic content quantified by the
melanopic/photopic (M/P) ratio (see below) of the SPD of light. As
such, a primary aspect of the present invention is to provide the
benefits of traditional circadian lighting without having to rely
heavily upon observable color changes provided by the singular use
of blue and red auxiliary lighting that produce the different
colored and circadian active light.
[0012] It was further discovered by vision scientists that
melanopsin receptors are absent in the central fovea of the eye,
but rather are distributed throughout the remaining retinal
body--which implies such receptors are not of concern for perceived
object brightness (i.e., brightness of a centrally viewed object
wholly confined to 2 degrees or less of visual field), but these
melanopsin receptors, as shown in Schlesselman et al., are
essential for quantifying background brightness (i.e., the
brightness of the overall space rather than the object). As such, a
primary aspect of the present invention is to provide benefits of
traditional circadian lighting while moving away from
state-of-the-art approaches which emphasize object brightness
(e.g., by considering only object luminance) as a control variable
in favor of the biologically effective background brightness.
[0013] Further objects, features, advantages, or aspects of the
present invention may include one or more of the following: [0014]
a. in terms of perceived color of background lighting, to provide
an imperceptible shift in color from lighting with a high melanopic
content to a low melanopic content or vice versa; [0015] b. to
provide said biologically effective lighting at a variety of
nominal color temperatures so as to, e.g., accommodate a number of
tasks and/or environments; and [0016] c. to provide said shift at a
constant perceived spatial or background brightness even though
their measured traditional illuminance varies.
[0017] A method according to one aspect of the present invention
comprises employing a single light fixture, module, luminaire, or
light source set to provide both general purpose or background
lighting and circadian lighting, wherein the light source includes
a first subset of sources such as LEDs with a high melanopic
content and a second subset of sources such as LEDs with a low
melanopic content of identical color (metameric lights) and wherein
the method comprises transitioning together in mixed concert from
the first subset of sources or LEDs to the second subset of sources
or LEDs according to a predetermined profile. A further method
according to aspects of the present invention comprises having said
high melanopic content have a relatively high percentage of energy
in the band around 488 nm, such as e.g. about 0.40 relative energy
normalized to 1.0; further e.g. where relative power is on the
order of 0.20 between 478 to 498 nm, on the order of 0.30 between
483 to 493 nm, and on the order of 0.40 between 486 to 490 nm, as
well as other values that may be derived from the examples of SPD
included herein or as may be appropriately developed.
[0018] An apparatus according to one aspect of the present
invention comprises an LED lighting fixture including said first
and second subsets of LEDs adapted and controlled to provide both
general purpose and circadian lighting.
[0019] A system according to one aspect of the present invention
comprises the aforementioned method in combination with the
aforementioned apparatus to produce an LED lighting system that
provides biological/physiological operational benefits while also
providing general illumination, and in a manner that does not
produce perceivably variable brightness or color.
[0020] These and other objects, features, advantages, or aspects of
this application of the present invention will become more apparent
with reference to the accompanying specification and claims.
III. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] From time-to-time in this description reference will be
taken to the drawings which are identified by figure number and are
summarized below.
[0022] FIG. 1A illustrates a simple lighting system according to
existing art in block diagram form.
[0023] FIG. 1B illustrates a more complex lighting system according
to existing art.
[0024] FIG. 1C illustrates a partial block diagram according to
existing art corresponding to FIG. 1B.
[0025] FIG. 2 illustrates in flowchart form one possible method of
designing a lighting system capable of both general purpose and
circadian lighting according to aspects of the present
invention.
[0026] FIG. 3A shows a computer graphic screen capture from a
calculation software application for use in the method of FIG.
2.
[0027] FIGS. 3B-E are renderings of the graphic of FIG. 3A
illustrating areas 100, 110, 120, and 130 of the image of FIG. 3A
in order to provide clear understanding of its content.
[0028] FIGS. 4A and B illustrate one possible LED lighting fixture
according to aspects of the present invention. (For illustrative
purposes only, FIG. 4A illustrates a light transmissive external
lens 5 by hatching and without showing the LED sources behind it,
but FIG. 4B shows how those LEDs would normally appear to a viewer
including with the lens in place.)
[0029] FIGS. 5A-D illustrate various possible apparatuses and
scenarios in which the LED lighting fixture of FIGS. 4A and B may
be employed to provide general purpose and circadian lighting
according to aspects of the present invention; note that for
clarity the external lens is illustrated with hatching indicating
light transmissivity.
[0030] FIG. 6A illustrates the melanopic spectral sensitivity
function overlaid with a SPD of a typical prior art white LED.
[0031] FIG. 6B is a table providing information about the spectral
functions represented in FIG. 6A.
[0032] FIG. 7 is a graph showing the relationship between the light
level values applied to regulate 2 different light sources used in
a lighting system according to aspects of the invention.
[0033] FIGS. 8A and B are graphs showing SPD for metamers having
high melanopic content according to aspects of the invention
[0034] FIG. 9 is a graphic representation of an operational profile
for lighting showing a transition from low M/P lighting to high M/P
lighting over time according to aspects of the invention.
[0035] FIGS. 10A-I are illustrations and graphs referred to in the
IES#1 and IES#2 sections infra.
IV. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0036] A. Overview
[0037] To further an understanding of the present invention,
specific exemplary embodiments according to the present invention
will be described in detail. Frequent mention will be made in this
description to the drawings. Reference numbers will be used to
indicate certain parts in the drawings. Unless otherwise stated,
the same reference numbers will be used to indicate the same parts
throughout the drawings.
[0038] Regarding terminology, reference has been given herein to
biological and/or physiological benefits associated with lighting;
particularly, circadian lighting. These benefits are widely
accepted as realized (as opposed to theoretical)--the use of the
terms "biological" and "physiological" are not intended to purport
any particular benefit as being more realized than another, nor
meant to disparage any particular benefit not widely accepted as
being realized. The aforementioned terms are used generically to
describe benefits that might be achieved by light induced circadian
entrainment, and more broadly, non-visual responses to lighting
that may relate to circadian lighting.
[0039] Further regarding terminology, reference has been given
herein to general purpose lighting and tasks that might be
performed thereunder. While some specific examples are given, the
use of the terms "general" and "task" are not intended to limit the
use or scope of the invention. General purpose lighting could be
exterior or interior lighting, with or without a specific task in
mind. The use of "general purpose" is also intended to provide a
cue with respect to perceived brightness; specifically, that
aspects according to the present invention are directed to
background brightness rather than object brightness (e.g., object
luminance), and so one is directed to consider the overall purpose
and environment of the lighting rather than primarily the color or
brightness of an object in one's central view. Whereas in the prior
art--including some of the sources included herein as
references--brightness is a term used colloquially and
interchangeably with luminance, this is not the definition of
"brightness" as used herein. Conceptually this can be likened to an
electronic device such as a tablet computer, phone, or gaming
device. Whereas prior art is describing brightness with respect to
a central object (e.g., how bright the letters on a tablet appear),
the present invention is describing brightness with respect to
everything outside of the central focus (e.g., how bright the
background on the tablet computer appears). While this may appear
to be a relatively small difference, it should be noted that the
effects of the melanopsin receptor are nascent and this new
approach to lighting design deserving of such delineation. And so
to avoid confusion, care has been given to use the terms
"illuminance," "luminance," and "perceived brightness" in
accordance with their widely accepted definitions within the
lighting industry, and barring that, in accordance with
Schlesselman et al.
[0040] Further regarding terminology, reference is given herein to
"perceived color"; namely, color that is perceived by the human eye
to be the same, regardless of whether it is produced by the same
specific detailed spectrum producing the light. As is described
herein, the invention makes use of metamerism; specifically, taking
advantage of the human visual response (i.e., the cones of the eye
responding broadly to SPD rather than at every possible visual
wavelength). As is well known in vision science and in the art of
lighting, it is widely understood that humans have three types of
cones which are responsible for initiating color perception (one
cone type each euphemistically referred to as red, green, and blue
cones) resulting in a characterization of a perceived color in
terms of neural computation based on the outputs of said cones. As
used herein, two sources characterized as having the same
"perceived color" are merely two sources which produce the same
overall stimulation of each of the three cones and therefore
perceived color, regardless of whether the source specific spectral
power distributions (SPDs) are identical.
[0041] Lastly regarding terminology, reference is given herein to
"melanopic content" as well as the relative melanopic content or
melanopic/photopic (M/P) value of the spectral power distribution
of a light source. While one or more visuals are later provided, to
give further definition to this term, one may consider melanopic
content for a light source of a given SPD as M, where M is
determined by convolving said SPD with a melanopic sensitivity
function (later described, also see FIG. 6A) which has been
normalized by a numerical value applied either (a) at its peak
wavelength (such as unity) or (b) to a numerical value of 683
applied at the wavelength of 555 nanometers consistent with the
traditional normalization of the photopic sensitivity function. M/P
is then determined by subsequently dividing that convolution by the
lumens associated with the same SPD. The result is a value obtained
in either effective milliwatts per lumen (mW/1m) for the unity
normalization or in the latter case a dimensionally homogeneous
number (i.e. melanopic lumens per photopic lumen). In either case
there is a fixed numerical conversion for all sources between these
normalizations or any other considered although the specific
conversion factor will depend on normalization choice. It should
also be noted that application of the invention herein described is
not limited to any specific normalization procedure.
[0042] As described herein, a high melanopic content light source
would have a higher M/P value and a low melanopic content light
source would have a lower M/P value when compared to one another;
further it should be noted that because this measure is a ratio
(M/P) it is independent of net light intensity. Thus, when
reference is given herein to "tuning" a light source, one is merely
changing the duty cycle or power input to LEDs (or other light
sources) having different M/P values but with a specific profile to
maintain color and perceived brightness. Additional information
regarding the measurement of perceived brightness and
melanopic/scotopic/photopic functions may be found in Schlesselman
et al.
[0043] The exemplary embodiment sets forth an LED lighting fixture
employing a plurality of LEDs some subset of which have higher
melanopic content than the others, operated according to a
predetermined profile so as to provide both general lighting and
circadian lighting without a perceivable shift in color or
brightness. The aforementioned LED lighting fixture could take a
number of forms--some of which are later described in greater
detail--but generally speaking may be described according to FIGS.
1A-C. At its core, an LED lighting system generally comprises a
power source 10 which distributes power via means 20 to a driver 51
which then distributes power which has been conditioned for use
with LEDs via means 21/22 to one or more fixtures 61. The general
principle illustrated in FIG. 1A is repeated and customized as
needed for a specific task or general purpose, the corresponding
lighting system becoming larger or more customized as needed; this
is illustrated in FIGS. 1B and C for a baseball field. As can be
seen from FIGS. 1B and C, a power source 10 generally comprises a
transformer (e.g., from a utility company) which provides
electrical power to a service distribution cabinet 30 via a
distribution wire 20. Said electrical power travels from service
distribution cabinet 30 to a control/contactor cabinet 40 via a
power line 21 where it further travels to a pole cabinet 50 housed
on each lighting support structure 60 (e.g. pole or other) via
power line 21, and finally powers one or more LEDs; note that for
clarity, only one complete circuit (from breaker 31 to contactor
module 41 to LED fixture 61 at Pole A) is illustrated in FIG. 1C.
The result is illumination of field 70. Of course, other
considerations are important to note, even in a generic LED sports
lighting system such as that illustrated in FIGS. 1B and C. For
example, grounding to protect against adverse electrical effects
(e.g., lightning) may be provided by earth grounds 80. Equipment
grounding may likewise be provided via equipment grounds 8 in
combination with ground wiring 82. Lastly, remote control
capabilities may be enabled via a remote control center 90 which
communicates wirelessly to a control module 42 via radio antenna 43
to provide dimming, on/off, or other scheduling information to
driver 51 via a gateway 44 in communication with a controller board
53 connected by communication means 22--which could comprise hard
wiring (e.g., RS-485, fiber), wireless communications (e.g.,
ZigBee), or could use existing wiring 22 in lieu of new wiring
(e.g., powerline communications). Remote control functionality such
as is described in U.S. Pat. No. U.S. Pat. No. 6,681,110,
incorporated by reference herein in its entirety, and commercially
available under the trade name CONTROL-LINK.RTM. from Musco Sports
Lighting, LLC, Oskaloosa, Iowa, USA, may be useful in implementing
predetermined operating profiles (e.g., power and/or duty cycle of
each subset of LEDs) remotely--whether timed, periodic, or on
command. Circuit breakers or fuses 52 could also be used to protect
the circuitry.
[0044] A more specific exemplary embodiment, utilizing aspects of
the generalized example described above, will now be described.
[0045] B. Exemplary Method and Apparatus Embodiment 1
[0046] As previously stated, according to aspects of the present
invention a single light source (e.g. fixture, module, or other
with a set of plurality of individual LED light sources) may be
produced wherein both general purpose or background lighting and
circadian lighting may be provided, and in a manner where
perceivable brightness (e.g., as measured by a true brightness
meter see below) and perceivable color are both constant over the
shift from an "awake" state to a "sleep" state. Said awake and
sleep state generally correlate to a low melatonin
production/metabolization rate and a high melatonin
production/metabolization rate, respectively; alternatively, said
awake and sleep state could be said to correlate to a more alert
state and a more sedate state, respectively. It should be noted
that it is not the primary purpose of the invention to determine if
circadian lighting actually provides a biological/physiological
benefit and if so, how to quantify or evaluate those benefits;
rather the invention further enables the practice of what is
becoming understood in the art to be beneficial aspects of
providing circadian lighting.
[0047] To provide both general purpose lighting and circadian
lighting from the same light source according to the present
invention a light source (see, e.g., LED fixture 61, FIGS. 1A-C and
4A-5D) is envisioned to comprise at least two subsets of LEDs FIG.
4B; a first subset 62 having a high melanopic content and white in
color, and a second subset 63 also white in color and having a low
melanopic content. These two said subsets are constructed as
metamers, i.e. they produce equal stimulation of the three cone
retinal receptors. Said metamers are produced from combinations of
specific LED's following the method of Vienot, F et al., (2012)
"Domain of metamers exciting intrinsically photosensitive retinal
ganglion cells (ipRGCs) and rods", Journal of Optical Society of
America A, February. 2012, Vol. 29, No 2, pp. A366-A376,
incorporated by reference in its entirety herein.
[0048] Based on present knowledge of the melanopsin efficiency
function, calculations including most catalogued white light
sources show that it is possible to achieve approximately a factor
of five (5) between a high M/P source and a low M/P source. Note
that this factor of 5 is a ratio and therefore is independent of
choices of normalization of the melanopsin sensitivity function
such as those introduced by Lucas et al
(http://lucasgroup.labls.manchester.ac.uk/research/measuringmelanopicillu-
luminance/website accessed 2016-05-25), incorporated by reference
in its entirety herein. Further, said first and second subsets of
LEDs must be of the same perceived color; namely, metamers of each
other, i.e. they produce the same net outputs for the three retinal
cones.
[0049] As such, according to a first step 1001 of a method 1000
(FIG. 2), a lighting designer or other person determines desired
correlated color temperature (CCT) properties of the envisioned
tunable, dual purpose LED circadian lighting system. Said lighting
designer or other person may evaluate the general purpose of the
lighting system (e.g., interior lighting, facade lighting, street
lighting) or a task to be performed thereunder (e.g., high detail
assembly work, general office work). This helps to inform what kind
of white background light is to be employed, as well as where
within the range of "white" the metameric pair of high M/P and low
M/P sources should exist.
[0050] Table 1 below can be useful for this design process and
illustrates CCT properties of several different well known light
sources (and in addition some developed according to aspects of the
present invention) with corresponding S/P and M/P values. M/P
values shown are based on using unity normalization at the peak
wavelength for the melanopsin sensitivity function. Values of M/P
based on the CIE type normalization are obtained by applying to the
M/P column in Table 1 the multiplicative factor 4.2146 based on the
melanopic function provided by the reference above (Lucas et
al).
TABLE-US-00001 TABLE 1 Source CCT S/P M/P High Pressure Sodium 1960
0.63 0.24 High Pressure Mercury 2970 0.81 0.29 Warm White 2850 1.03
0.43 Warm White 2900 1.09 0.47 Metal Halide 27k 2650 1.16 0.53
Metal Halide 32k 3320 1.36 0.63 Metal Halide 30k 2910 1.38 0.65
Metal Halide 37k 3440 1.48 0.70 Metal Halide 40k 3880 1.54 0.73
Lite White 4250 1.49 0.70 RE Compact Fluorescent 3170 1.19 0.48
White Fluorescent 3540 1.26 0.56 Ultralume Fluorescent 3130 1.28
0.55 Cool White 4060 1.30 0.57 Cool White Deluxe 4270 1.79 0.89 LED
Lamp 5500 2.09 1.11 Daylight Fluorescent 5140 2.09 1.07 Fluorescent
65k 6380 2.26 1.18 GE75 9530 2.62 1.43 M/P LED 17000 3.31 1.66 M/P
LED 5700 2.51 1.18 Musco (1) LED 2400 2.6 1.43 Musco (2) LED 3100
1.2 0.52
[0051] If desired, additional color properties could be considered
according to step 1001 of method 1000. For example, if an
identified task requires accurate color rendering, a lighting
designer or other person may opt to also define a relatively high
(e.g., .gtoreq.60) color rendering index (CRI).
[0052] FIGS. 8A and 8B are graphs showing SPD for light sources
Musco (1) and Musco (2), according to aspects of the invention and
as referenced herein.
[0053] According to a second step 1002 of FIG. 2, the desired
melanopic content range (i.e., the high melanopic content and the
low melanopic content) are chosen. It is important to note that the
melanopic content range can be chosen to be approximately within a
single CCT if the ambient light is considered as important for task
color fidelity. The choice of one melanopic content range over
another may depend, at least in part, on manufacturability.
[0054] It should be noted that to fulfill the requirement of a
melanopic efficient light source, LED designers would need to
discontinue the practice of overlooking a key portion of the
spectrum (around 488 nm), At one time, this portion of the spectrum
was generally considered unimportant, since it was believed not to
materially contribute to visual acuity, color rendering, etc.; now
it is better understood to be a required factor to activate the
melanopsin receptor. For example, FIG. 6A shows the "melanopic
function" superimposed on the spectral function for a typical 5700K
LED source. FIG. 6B shows values related to the curves of FIG. 6A.
In this case, the peak of the melanopic curve is nearly perfectly
aligned with a drop in the LED spectral curve such that this
typical LED source can be seen to contain very low relative
melanopic content, and therefore would not provide the benefits of
high melanopic content light.
[0055] It is believed that the metamers ("Musco (1)" and "Musco
(2)") reported on in the last two rows of Table 1 and used by
Schlesselman et al can also be produced as a viable commercial
light source using state-of-the-art practices related to LED
phosphors. It should be noted that the invention as envisioned
comprises at least a light source which has a relatively high
percentage of energy in the band around 488 nm. In the case of the
Musco (1) source, this is at about 0.40 relative energy with total
energy normalized to 1.0 in the visible range. Thus, it may be seen
that a high relative value for light at 488 nm, as well as light
near the 488 nm value such as from 486 to 490 nm, 483 to 493 nm, or
even from 478 to 498, or a still even broader range such as from
468 to 508 nm, especially when included specifically to increase
melanopic content for a certain time period, while maintaining
perceived brightness and color relative to a metameric light source
having much lower melanopic content, is of high value in the
industry. Specific examples of relative power envisioned include at
least on the order of 0.20 between 478 to 498 nm, on the order of
0.30 between 483 to 493 nm, and on the order of 0.40 between 486 to
490 nm, as well as others that may be derived from the examples of
SPD included herein or as may be appropriately developed.
[0056] Following step 1002, an optional step 1003 comprises
verifying that the high melanopic content LED either by the
manufacturer or independently through specialized field meters is
actually a metamer of the low melanopic content LED and vice versa
for the intended use; namely, that their SPDs are different but
that they provide the same net cone stimulation and thus that the
perceived ambient light will have same color. FIG. 3A shows a
graphic screen capture from a calculational software application
which might be used in optional step 1003. FIGS. 3B-E provide a set
of renderings of the graphic of FIG. 3A illustrating areas 100,
110, 120, and 130 of the image of FIG. 3A in order to provide clear
understanding of its content.
[0057] A fourth step 1004 comprises establishing a constant
perceived brightness between the high melanopic content LED and the
low melanopic content LED as the overall melanopic output of the
combined system varies according to a specific user schedule. As
previously discussed, the recently discovered melanopsin
receptor--more specifically, the intrinsically photosensitive
retinal ganglion cells (ipRGCs)--has been observed to impact
perceived brightness. Perceived brightness, as previously stated,
is not the same as luminance or illuminance (despite language that
may not state this clearly in some of the included references).
Perceived brightness for a space is understood in accordance with
Schlesselman et al., as the brightness sensation associated with
the lighting of a large space (compared to centrally viewed
objects) such as a room or an athletic field or even device
background area. In general, such spatial brightness depends on
both cone and melanopsin reception and has been determined by
Schlesselman et al. as above to be described by augmenting the
traditional output of the cones noted as P by the multiplicative
factor (M/P)z., where the exponent z depends on the particular
viewing conditions. For the conditions of a lighted sports field,
Schlesselman et al above have empirically determined that the
exponent has the value 0.32.+-.0.02 and has also been determined to
be approximately the same for typical architectural environments.
For other visual environments such as computer screens and mobile
phones the exponent is also expected to be similar but could differ
slightly. These concepts are shown explicitly by Equations 1 and 2
below that provide the auxiliary multiplicative factor that
correlates with full or `true` spatial brightness perception
associated with the melanopic effect. The multiplicative factor as
applied to the standard photopic illuminance quantity P for the
general visual conditions described above.
[0058] General Case:
Spatial Brightness B=P(M/P).sup.z Equation 1
[0059] Special Cases as Described Above:
Spatial Brightness B=P(M/P).sup.0.32 Equation 2
[0060] Thus, in general, if two sources with different M/P values
(e.g. LED.sub.1 and LED.sub.2) are to produce the same spatial
brightness then their respective photopic illuminances are adjusted
following equation 1 as
LuxLED1/LuxLED2=[M/P.sub.LED2/M/P.sub.LED1].sup.z Equation 3
which may be restated as:
LuxLED2/LuxLED1/[M/P.sub.LED2/M/P.sub.LED1].sup.z Equation 3
For the conditions of a lighted athletic field or for general
architectural environments the general exponent `z` is replaced by
the numerical value 0.32 i.e. equation 3 becomes
LuxLED1/LuxLED2=[M/P.sub.LED2/M/P.sub.LED1].sup.0.32
LuxLED2/LuxLED1/[M/P.sub.LED2/M/P.sub.LED1].sup.0.32 equation 4
For the direct measurement of full spatial or `true` brightness in
the field, software is introduced into a traditional light meter to
include incorporating the M/P values to adjust its output to
provide a field measurement of `true` brightness (thereby creating
a spatial or "true" brightness meter). In particular, such a meter
would use the dimensionally homogeneous M/P values based on the CIE
type normalization where, in one example, the melanopsin
sensitivity function has the value 683 at the wavelength of 555 nm.
However, since the percentage difference of photopic lux between
the two systems depends only on ratios of M/P values as per
equations 3 and 4, that percentage is independent of the
normalization method. It should be further noted that Schlesselman
et al. as above have also shown that the exponents mentioned above
are independent of normalization procedure.
[0061] As numerical examples of applying equation 4 and as an
example of demonstrating the utility of the results of Schlesselman
et al in terms of possible lighting energy savings, one may
consider two cases of sources each generically for `LED1` and
`LED2` based on the values provided in Table 1 with approximately
equal CCT values, namely "cool white" with "cool white deluxe" and
"Metal Halide 27K" with "Musco (1)". For each of these cases,
assuming the lower M/P source provides 100 Lux of ambient
illumination, the higher M/P sources achieve the same brightness
perception with approximately 87 Lux or 73 Lux respectively. These
latter values can be verified as producing equal brightness
perception with the aforementioned spatial brightness meter. The
particular numerical values are calculated using the second form of
Equation 4 as follows:
For LED1=cool white and LED2=cool white deluxe
Lux.sub.LED2=Lux.sub.LED1/[M/P.sub.LED2/M/P.sub.LED1].sup.0.32
Lux.sub.cool white deluxe=Lux.sub.[cool white]/[M/P.sub.cool white
deluxe/M/P.sub.cool white].sup.0.32 Lux.sub.cool white
deluxe=100/[0.89/0.57].sup.0.32 =86.7 Lux
For LED1=Metal Halide 27k and LED2=Musco (1)
Lux.sub.LED2=Lux.sub.LED1/[M/P.sub.LED2/M/P.sub.LED1].sup.0.32
Lux.sub.Musco(1)=Lux.sub.Metal
Halide27k/[M/P.sub.Musco(1)/M/P.sub.Metal Halide27k].sup.0.32
Lux.sub.Musco(1)=100/[1.43/0.53].sup.0.32=72.8 Lux
[0062] Knowing the photopic illuminance of both the high and low
melanopic content sources (such as LEDs) to achieve the same
perceived brightness, one may determine appropriate power inputs
associated with said illuminances (i.e., the current needed to
power the low and high melanopsin sources at their appropriate
light levels). Determination of a power input to obtain a desired
photometric output and measuring light using a light meter is well
known in the art; of course, a traditional light meter could be
used to verify that both the high and low melanopic content LEDs
are operating at their desired photopic illuminance to achieve the
desired energy savings.
[0063] For the invention proposed where the application is for
dynamically controlling circadian stimulation, equation 3 serves as
the indicator of the initial and final illuminance levels of the
two metameric sources (high and low circadian stimulation) that
assure equality in brightness perception. Dynamically and over the
operating time period such stimulation moves from maximum
stimulation (high M/P, e.g. LED1) to minimum stimulation (low M/P
e.g. LED2). During the transition period, the illuminance values of
both LED1 and LED2 are adjusted simultaneously to maintain constant
brightness perception while constant color is assured during the
transition as the 2 sources are metamers and thus any mixture of
these metamers will retain the same color.
[0064] The algorithm for the illuminance profile for the two
sources operating simultaneously in concert to achieve both
constant color and brightness perception during the transition is
set forth in equation 5 below.
(F.sub.LED1+F.sub.LED2)*[(F.sub.LED1+cFLED2)/(F.sub.LED1+F.sub.LED2)].su-
p.z=1 Equation 5 [0065] where: FLED1=fractional photopic
illuminance of the high melanopic content source calculated in
Equation 1, and 0<F.sub.LED1<1 [0066] FLED2=fractional
photopic illuminance of the low melanopic content source calculated
in Equation 1, and 0<F.sub.LED2<c.sup.-z [0067] c=[
M/P.sub.LED2/M/P.sub.LED1], and covering a wide range of
possibilities, 1/4<c<4
[0068] Equation 5 should be considered as a timed function--namely,
that as power adjustments are made to LED1 to change its circadian
efficiency, compensating power adjustments are made to LED2 to
assure overall brightness perception associated with the total
source pair remains constant. A user schedule may be applied such
as changes every few minutes, in accordance with an existing
building management system, or in accordance with local
sunrise/sunset times, as a few non-limiting examples. Table 2 shows
an example of such a power profile that could be used to vary
melanopic content over time. As will be appreciated, other profiles
based on other parameters are possible, according to need or
desire.
[0069] For example, the operating profile of Table 2 (see also FIG.
9) could basically be the reverse. Instead of an 8 hour work shift
starting at 8 PM, it could start at 8 AM. The % High M/P vs. % Low
M/P would be reversed (e.g. at 8 AM 100% High M/P and 0% Low M/P).
The profile would proceed to 9 AM and transition to 75% High M/P
and 25% Low M/P, 11 AM 50% High M/P and 50% Low M/P, 1:00 PM 25%
High M/P and 75% Low M/P; and 3:00 PM and 4:00 PM at 0% High M/P
and 100% Low M/P.
TABLE-US-00002 TABLE 2 Time (e.g. over an 8 hour work shift) % High
M/P % Low M/P 8:00 PM 0 100 9:00 pm.sup. 25 75 11:00 PM .sup. 50 50
1:00 AM 75 25 3:00 AM 100 0 4:00 AM 100 0
[0070] FIG. 9 shows a similar profile graphically representing a
transition from low M/P light to high M/P light stepwise from 8 pm
to 4 am changing from 100% low M/P light at 8 pm through 25%, 50%,
75%, and 100% high M/P light at 9 PM, 11 PM, 1 PM, 3 PM, and 4 PM
respectively.
[0071] Equation 5 can also be specialized to the viewing conditions
of a lighted athletic field or general architectural environments
where the exponent takes on the value z=0.32 in which case equation
5 becomes equation 6 below:
(F.sub.LED1+F.sub.LED2)*[(F.sub.LED1+cF.sub.LED2)/(F.sub.LED1+F.sub.LED2-
)].sup.0.32=1 Equation 6
[0072] To illustrate the effects of using various values for e.g.
F.sub.LED1+F.sub.LED2, FIG. 7 is a graph (using values `f1`, `f2`,
and `c` corresponding to FLED1, FLED2, and the exponent 0.32
respectively as used in Equations 4 and 6showing the concomitant
fractional change in f2 (=F.sub.LED2) to maintain equal brightness
and color as f1 (=F.sub.LED1) changes from unity to zero per
prescribed schedule for some listed values of the constant `c`
(Equation 5).
[0073] Thus, when the illuminance of the initial source (e.g. high
circadian stimulation) is chosen based on particular design
criteria, and once the power input to achieve said output is known,
one utilizes the associated power control profile according to step
1005 of method 1000 to adjust the complimenting metameric source so
that the net light from 2 sources in consort achieve constant
perceived brightness while the circadian stimulation is varying.
Said power profile could be readily implemented via software or
communicated from an offsite position to a controller board for an
associated subset of LEDs--for the scenario in FIGS. 1B and C from
a remote control site 90 to antenna 43, to gateway 44, along
communication means 22 to controller board 53, and finally to
drivers 51. Said power profile could transition from the high
melanopic content LEDs to the low melanopic content LEDs according
to some regular period (e.g., a 1% power input change resulting in
some fractional illuminance output change every several minutes),
on demand (e.g., via manual power adjustment member such as a
rheostat), or otherwise such as a pre-programmed schedule. So it
can be seen that method 1000 sets forth a more comprehensive way of
designing circadian lighting systems as compared to
state-of-the-art practices insomuch that not only is color
considered (i.e., the cone response), and not only are circadian
rhythms considered (i.e., the biological/physiological response),
and not only is brightness considered (i.e., the additionally
controlled melanopic response), but all three are taken into
account--and in a manner that maintains a perceivably constant
color and spatial brightness perception. Method 1000 may be
embodied in a variety of apparatuses so to produce a dual purpose
LED lighting system (i.e., providing both general purpose lighting
and circadian lighting); one such apparatus is illustrated in FIGS.
4A and B.
[0074] As can be seen from FIGS. 4A and B, LED fixture 61 generally
comprises an array of LEDs; here 84 LEDs wired in two parallel
strings (with 42 LEDs each wired in series) but physically spaced
within the fixture such that the LEDs alternate from high melanopic
content to low melanopic content. So looking at FIG. 4B, the first
LED in the top row, upper left corner may be a high melanopic
content LED, the next one to it may be a low melanopic content LED,
the next one a high melanopic content LED, and so on. Alternating
physical placement of the two subset of LEDs in this manner ensures
the beam pattern and light uniformity (which is critical for
general purpose and tasks performed thereunder) is maintained as
the high melanopic content LEDs which are at full output in the
morning are transitioned to low or no output in the evening (and
vice versa for the low melanopic content LEDs). It should be noted
that control of two separate strings would require either two
drivers or a single driver with two outputs, but these are readily
commercially available and in many cases are still a lower cost
option to a user than having to purchase a general purpose lighting
system and a circadian lighting system.
[0075] LED fixture 61 further comprises a fixture housing 11
constructed of aluminum (or other thermally conductive alloy) with
integral finned heat sink 6, which together with transparent lens 5
at each (or selected) LEDs 1, encloses the LED light sources and
optics panel 7 with interchangeable optics 8. LED fixture 61 could
be used with a variety of support structures so to enable operation
in a variety of environments or for a variety of tasks. In addition
to a sports lighting application such as that illustrated in FIGS.
1B and C, LED fixtures could be ground mounted for architectural
lighting (FIG. 5A), affixed to a strapping device which could be
further affixed to an existing feature (e.g., tree) for temporary
or event lighting (FIG. 5B), mounted to an adjustable jig for
mobilized, targeted lighting (FIG. 5C), or recessed for general
purpose interior lighting (FIG. 5D). Of course, other applications
are possible, and envisioned--and any of the aforementioned
applications may have different requirements to fully realize the
desired biological/physiological benefits of circadian lighting.
For example, while the arrangement of FIG. 5A could be used to
illuminate outdoor sculptures (e.g., at an outdoor art event) and
where the low melanopic content lights are gradually becoming more
dominant near closing time (e.g., to provide a non-visual cue to
patrons to leave and "wind down" for the evening), the opposite may
be appropriate for a night worker at a port using the arrangement
of FIG. 5C. It may be preferable to start with the low melanopic
content LEDs fully powered and increase the dominance of the high
melanopic content LEDs over the course of a night shift (e.g., to
encourage alertness). Either of these scenarios may benefit from
aspects according to the present invention.
[0076] The invention may take many forms and embodiments. The
aforementioned examples are but a few of those. To give some sense
of some options and alternatives, a few examples are given
below.
[0077] C. Options and Alternatives
[0078] The present invention sets forth methods, apparatus, and
systems for providing both general purpose lighting and circadian
active lighting from the same lighting system. It is important to
note that this does not place a limitation on the use of aspects
according to the present invention. A person could operate a
lighting system according to aspects of the present invention (e.g.
a lighting system having both high melanopic content sources and
low melanopic content sources or even a single source whose
spectral output can be dynamically adjusted) so as to output any
desired melanopic content within the range of the included sources;
this could range from utilizing from 0 to 100%, or anywhere in
between, of the high melanopic content sources and from 0 to 100%,
or anywhere in between, of the low melanopic content sources
according to a schedule that could include any interval of timing
of any of the melanopic content selections even up to 100% duty
cycle at any of the extremes (i.e. ranging from operating full time
at 100% high melanopic content to 100% low melanopic content
sources or any set point in between these extremes) and not deviate
from aspects of the present invention.
[0079] With regards to the various formulas set forth, it should be
noted that these could differ and not depart from at least some
aspects according to the present invention. For example, since
melanopsin/melanopic content is a relatively new concept in the
field of vision science, it may be preferable to use a different
ratio to represent the non-visual response to perceived brightness
(even if not a perfect substitution under all testing conditions).
It has been found (see Schlesselman et al) that melanopic content
is highly correlateable to the ratio of scotopic to photopic
outputs (S/P) rather similarly to M/P--where S represents the
convolution of the source SPD with the scotopic luminous efficiency
function(V'(.lamda.)) as sourced from the Commission internationale
de l'eclairage (CIE) . The high correlation between S/P and M/P
allows the data to be analyzed with S/P as the functional spectral
factor just as well as M/P. In such an instance, Equation 3 would
be modified to become Equation 7 and Equation 6 would be modified
to become Equation 8.
Lux.sub.LED1/Lux.sub.LED2=[S/P.sub.LED2/P.sub.LED1].sup.0.436
Equation 7 [0080] where: Lux is measured photopic luminance
[0080]
(F.sub.LED1+F.sub.LED2)*[(F.sub.LED1+dF.sub.LED2)/(F.sub.LED1+F.s-
ub.LED2)].sup.0.436=1 Equation 8 [0081] where: FLED1=fractional
photopic illuminance of the high melanopic content source
calculated in Equation 1, and 0<F.sub.LED1<1 [0082]
FLED2=fractional photopic illuminance of the low melanopic content
source calculated in Equation 1, and
0<F.sub.LED2<c.sup.-0.436
[0082] d=[(S/P.sub.LED2)/(S/P.sub.LED1)], and 1/5<c<5
[0083] As another example, instead of timed power adjustments
(e.g., where input current is increased or reduced), timed duty
cycles of prescribed sources may be adjusted to facilitate a
transition from a high melanopic content source to a low melanopic
content source and vice versa.
[0084] D. IES#1 (Supplemental Information)
[0085] Brightness judgments in a simulated sports field correlate
with the S/P value of light sources.
[0086] Bradley Schlesselman, Myron Gordin, Larry Boxler.sup.1,
Jason Schutz, Sam Berman.sup.2, Brian Liebel.sup.2 and Robert
Clear.sup.2
[0087] Musco Sports Lighting, LLC, 100 1.sup.st Avenue West,
Oskaloosa, Iowa 52577
[0088] Abstract:
[0089] Brightness perception in a simulated sports field was
evaluated for photopically equal and constant color lighting but of
different spectral content (metamers). A simulated sports field of
dimensions 20.times.30 feet was constructed in an enclosed space
and lit to the distribution of photometric conditions (both light
and dark) approximating those measured at night in an operating
full size illuminated sports field. Fifty-seven subjects comprising
3 age groups (18-30 years, 31-50 yrs and >50 years) were
selected and sat in a chair positioned at an edge and midpoint of
the simulated field, providing a binocular and unobstructed view of
both the lit "field" and dark surround. The illuminance levels were
60,150, and 400 vertical lux at eye level in the direction of gaze,
corresponding to those measured for spectators and performers in an
operating field. Subjects were Musco employees or their family that
had no special knowledge in lighting and were unaware of the study
purpose. The study utilized theatrical luminaires with multiple and
different colored LED sources which could be combined to form four
pairs of whitish metamers, each pair consisting of one metamer
having a relatively higher S/P ratio compared to the other. Two
pairs had relatively higher nominal CCT values than the other two
pairs, and within each CCT set of metamers, one pair had a wide
spread between the high and low S/P ratio metamer, while the other
pair had a relatively smaller difference between the S/P ratios.
The S/P values ranged approximately from 1.2 to 4 and the
difference between the S/P values for a compared pair varied
between 0.72 and 1.86. The conventional CCT values ranged from
nominal 2700K to 6700K.
[0090] Subjects compared the perceived brightness of the
illuminated field under each metameric pair where the illuminance
measured at the eye was equal for each of the two sources within
the compared pair. The comparison was judged while subjects viewed
repeated switching between the paired lightings. Subjects were
asked to focus on an iPad mini with a video image of a lava lamp
placed in the middle of the simulated field, and judge which of the
2 lighting conditions appeared brighter. 47 Subjects completed this
test that included all four metameric pairs at both 60 and 150 lux,
and one pair at 400 lux, for a total of 423 total spectral
comparisons. The result obtained was that 375 out of those 423
comparisons had the higher S/P value light sources chosen as the
lighting that gave the illuminated field a brighter appearance.
This result yields an unbiased estimate of 88.5%.+-.1.6% in favor
of the higher S/P as perceived brighter with a miniscule p-value or
probability of chance occurrence of approximately 10.sup.-134. The
results were highly significant for all age groups.
[0091] To establish a possible objective correlate associated with
the brightness perceptions, pupil size was measured employing
infrared pupilometry for two of the metameric pairs at the 150
vertical Lux light level for 40 subjects. Results showed that on
average pupil sizes were significantly smaller for the higher S/P
spectra under otherwise identical lighting conditions, and were
also in quantitative agreement with past observations although not
necessarily the causal factor in brightness perception.
[0092] Background:
[0093] Previous studies Berman et al (1990), Brown et al (2012),
Royer &Houser (2012) have shown that in conditions of full
field of view lightings of the same color but of different spectral
content and also with equal photopic luminance (metamers) are not
perceived as equally bright. Current understanding of these
observations [Brown et al (2012), Ecker et al, (2010)] is that they
are likely a result of the responses of the non-image forming
melanopsin photoreceptor widely distributed in the retina of the
eye and whose spectral responses are not included in the
determination of photopic luminance. Earlier work by Berman et al
(1990) and prior to the discovery of the melanopsin receptor
correlated full field brightness perception with the spectral
content of metamers by employing an empirically determined
correlation based on the S/P value of the metamer spectral content.
Later calculations showed that for polychromatic light sources
typical of lighting practice that there was a very high correlation
(over 99%) between the S/P values and the melanopic content of
these sources [Berman (2008), Berman &Clear (2008,2014)].
Although recent research [Royer &Houser (2012)] determined that
photopic luminance did not predict equal brightness perception for
their metamers, it was also concluded that the use of S/P failed as
the spectral factor for correlating their results leaving
uncertainty as to both the mechanisms behind the brightness
perceptions and a practical guidance for lighting practice.
[0094] Study Objectives:
[0095] Over the past several years Musco engineers noticed that
their brightness perceptions of lit athletic fields appeared to
depend on the spectral content of the lighting. Such perceptions
could possibly be due to vision related color effects resulting
from differences in source colors (Harrington 1954), or effects of
differences in source melanopic content (Bailes 2010) or perhaps a
concurrence of both effects. In view of the past research efforts
described above it was the intent of Musco to conduct a study where
the 2 visual percepts were separated and to first examine the
non-color effects. Thus, the objectives of this investigation were
to provide a more rational explanation of the field observations in
terms of the most current lighting and vision science.
[0096] Methods:
[0097] Description of Test Room:
[0098] In order to accomplish these objectives a test room was
designed to provide a reasonable simulation of an existing athletic
field. A recreational soccer field of dimensions 240 feet by 150
feet lit to conventional light levels was chosen as a typical real
field from which to design the simulation. Measurements of vertical
illuminance at the eye were taken at this representative field from
the perspective of a player in the field and a spectator on the
side, yielding nominal values of about 150 and 60 vertical Lux
respectively corresponding to a range of 250 to 300 Lux of
horizontal illuminance. The visual lighting perspective gained by a
person standing on one side of the field and at the midpoint would
provide a view with approximately 3/4 of the total visual solid
angle as essentially dark and the remaining lit by the field
luminaires.
[0099] A 30` wide by 20' deep simulated test field was constructed
inside a large hall, lit so that about 3/4 of the visual solid
angle was in the dark from the perspective of the subject situated
at the midpoint of the longer dimension and at the front end of the
shorter dimension. The design of the simulated field was based on
actual field condition sight lines. FIGS. 10A, 10B and 10C show a
perspective view of the simulated field construction, a
cross-sectional drawing, and a photograph, respectively, of the
test environment. The simulation of the field was accomplished by
lighting only the lit portion of the test floor, which was painted
a spectrally neutral, matte gray color and had an incline of 7.5
degrees to establish concordance in the end point viewing angle of
the subject as would occur on the real field. The dark portion was
obtained by using matt black fabric that was placed to surround the
lit portion of the test space.
[0100] Achieving the necessary illuminance to simulate the field
conditions required both direct lighting on the test field floor
plane to yield a field luminance distribution approximating that of
the real sports field, along with the addition of several overhead
fixtures that provided the majority of vertical illuminance at the
observer eye that would come from typical high mast sports lighting
luminaires in real conditions. Attention was paid to assure that
these overhead fixtures were not directly visible by the subject as
well as to minimizing possible direct glare due to the proximity of
these overhead fixtures in relation to the subject position (see
FIGS. 10A-E).
[0101] For the study, subjects sat in a chair at the midpoint of
the long dimension at the edge of the lit floor as seen in FIG. 10C
and viewed an iPad Mini tablet placed in line with center of the
long dimension and at the middle of the lit floor. The iPad screen
subtended essentially a foveal visual angle of about 3 degrees from
the subject position and provided a fixation point. The iPad was
set to display slow temporal screen variations by showing a
simulated lava lamp scene of fixed color thereby helping to reduce
boredom and to assure that the direction of gaze would be similar
for all subjects. The iPad was placed in the center of a 12 inch
diameter black circle (FIGS. 10C and 10D) and together these
essentially foveal objects help to minimize the transient `Maxwell
Spots` that can be sensed in the central visual field when
switching between test metamers and when the lit field of view
extends much beyond the fovea.
Lighting System:
[0102] The lighting for the test facility was provided by
theatrical fixtures suitably placed so that the lighting
distribution on the floor was uniform (10 fixtures), with an
additional 5 fixtures adjusted to achieve the illuminance at the
eye in the direction of gaze (DOG illuminance), namely the test
values of 60 and 150 Lux. At maximum output it was also possible to
achieve a higher value of approximately 400 DOG Lux and some
testing was undertaken at that higher level.
[0103] The fixtures were ETC Source Four LED theatrical luminaires
with an array of 60 Luxeon Rebel emitters that consisted of 7
spectrally different colored LEDs (See FIG. 10E for a photo). The
specific spectral power distributions (SPDs) were chosen so that
several overall whitish metamers could be obtained but with
different S/P content and CCT values (see section below on metamer
design). A programmable DMX controller was used to yield the
particular light levels and metamer combinations, where the LED
light level output had a linear relationship with DMX value. The
DMX controller allowed for rapid switching between metamers that
would eventually be compared for brightness perception with a total
transition time interval of 1 second. In addition, the controller
allowed metamerism to be maintained during the switching with a
gradual shift in S/P values to its end point value by transitioning
over 5 intermediate metameric stages each of 200-millisecond
interval thereby minimizing transient perceptual effects.
Metamer Design:
[0104] The goal was to create whitish metamers of different
melanopic spectral content or analogously different S/P spectral
content as employed in the earlier studies by Berman et al (1990)
and Brown et al (2012). Since color differences will contribute to
brightness perception even at equal photopic luminance, the
revealing of possible non-cone mechanisms requires that the viewed
scenes of different spectral content have identical cone
stimulation and therefore perceived color but have different
melanopic or equivalently S/P content.
[0105] Typically source metamerism is determined by employing the
conventional CIE color space such as the CIE 1931 2.degree. or CIE
1964 10.degree. observer color space and this was indicated as the
procedure used by Royer &Houser (2012). There are however,
deficiencies in the conventional CIE color matching functions when
applied to forming perceived metamers that have been previously
noted in the literature (Boynton 1996, Shaw 1999). In particular,
Stockman & Sharpe (1996,1999,2000) have presented an
alternative color space that addresses those deficiencies. The cone
fundamentals of the alternative color space are detailed in CIE
(2006) "Fundamental chromaticity diagram with physiological
axes--Part 1 Technical Report 170-1". For the purposes of this
study metamerism is obtained by equal stimulation of those cone
functions for the metamers and was determined for the 7 LED sources
by employing the methodology described by Vienot et al (2012) as
based on Cohen & Kappauf (1982,1985). These constructions
provide much superior perceived metamers when compared to
constructions based on the CIE protocol of equal
chromaticities.
[0106] Note that the CCT values associated with the metamers and
indicated in this study are calculated by employing the
conventional CIE chromaticity system as applied to the SPD's of the
test metamers and are referred to here as conventional or
traditional CCT values. Since these test metamers do not have
precisely equal CIE chromaticity values our calculated CIE CCT's
will also be different for a compared metamer, but even so
observers do not perceive color differences as metamers based on
the Stockman/Sharpe functions are perceived as more identical. On
the other hand, should alternate CCT values based on a color space
employing the Stockman/Sharpe cone fundamentals be evaluated then
those alternate CCT values would be identical for metamers
constructed from those fundamentals. FIG. 10F shows the location of
our metamers on a conventional chromaticity diagram where the
slight shifts from chromaticity equality are indicated.
[0107] Four metameric pairs were constructed using the combination
of LEDs within the ETC fixtures. The pairs were designed such that
two pairs had a relatively higher conventional CCT than the other
two pairs, and within each of the two pairs with differing
conventional CCTs there was one pair with a wide spread between S/P
values and one pair with a smaller spread between S/P values. The
resulting metamers are described below in the following tables and
figures: [0108] Table 1 indicates the CIE x,y chromaticity
coordinates of the (7) LED's and the resultant (8) metamers [0109]
FIG. 10F shows the locations of Table 1 values on a conventional
CIE chromaticity diagram [0110] FIG. 10G shows a graph of the SPD's
of the (7) LEDs that compose the metamers and listed in Table 1
[0111] FIG. 10H shows a spectral graph of the (8) metamers listed
in Table 1
TABLE-US-00003 [0111] TABLE 1 CIE x, y Coordinates of the seven LED
sources and the resultant metamers. CIE CHROMATICITY COORDINATES
ETC LED Sources X Y Amber 0.5700883 0.4254393 Blue 0.1283426
0.0719665 Cyan 0.0747183 0.4494363 Green 0.2152694 0.7123734 Indigo
0.1549665 0.0244588 Red 0.6914472 0.3060068 White 0.3321667
0.3485219 Metamer Pairs S/P Code X Y Pair 1 High CCT Hi HWH
0.3277019 0.2778902 Wide S/P Spread Lo HWL 0.3086062 0.3341716 Pair
2 High CCT Hi HSH 0.3167614 0.3053155 Small S/P Spread Lo HSL
0.3097961 0.3278254 Pair 3 Low CCT Hi LWH 0.4534897 0.3622677 Wide
S/P Spread Lo LWL 0.4322281 0.4145167 Pair 4 Low CCT Hi LSH
0.4430859 0.3839001 Small S/P Spread Lo LSL 0.4348558 0.4085055
Lighting Conditions:
[0112] Each metameric pair was established, including the
incremental steps, using the method described above. Once the
fixtures were put in place to achieve the uniformity and Direction
of Gaze (DOG) illuminance targets to simulate the sports field
conditions, light measurements were taken to record the SPD and
resultant S/P ratio and CCT of each metamer. Table 2 summarizes the
measured values of the metamers:
TABLE-US-00004 TABLE 2 Lighting Conditions: Vertical DOG
Illuminance, S/P values and CCT values Illuminance Levels
Illuminance Levels 60 150 400 60 150 400 Pair Description Code S/P
S/P S/P CCT CCT CCT 1 High CCT HWH 3.952 3.898 5653 5475 Wide S/P
HWL 2.088 2.064 6580 6380 Spread Delta 0.942 0.881 0.820 -262 -364
-442 2 High CCT HSH 3.087 3.009 2.937 6444 6224 5992 Small S/P HSL
2.145 2.128 2.117 6706 6588 6434 Spread Delta 0.942 0.881 0.820
-262 -364 -442 3 Low CCT LWH 2.610 2.599 2389 2373 Wide S/P LWL
1.222 1.239 3109 3149 Spread Delta 1.388 1.36 714 -776 4 Low CCT
LSH 2.098 2.073 2713 2688
Lighting Measurements:
[0113] Throughout the testing procedure, lighting measurements were
taken to ensure that light level and color consistency was
maintained for each testing condition using a Gigahertz Model#
BTS256-E BiTec Sensor Luxmeter. The meter was positioned to measure
the vertical illumination at the eye in the Direction of Gaze (DOG
illuminance), as well as the Spectral Power Distributions received
at the eye. The S/P value was calculated from the measured SPD for
each lighting measurement taken. The meter provided output data
into a computer file that recorded the measurements for all tests,
and these measurements were reviewed for each subject and for each
test.
[0114] In some cases, the results of the light measurements showed
departures from the constant value desired, including some cases
where the recorded value was zero. During the data analysis, some
subject's data did not meet the consistency required (constant DOG
illuminance or S/P values, for instance), and those subjects were
consequently excluded from the analysis. The consistency for
constant illuminance and S/P values for the experiments was
reviewed for both within and between subject analyses. The design
of the test with regard to the lighting measurements was considered
critical to ensure that the subjective judgments reported by the
subjects was in fact based on the lighting values that were
programmed into the lighting control system.
Subject Selection:
[0115] Subjects were volunteer Musco employees or their family
members who satisfied general and normal visual behaviors but were
rejected if such conditions as ocular disease, color blindness, or
tinted contact lenses were present. In addition, qualified subjects
were not medicated regularly with pain reducers, especially
opiates, and were over the age of 18 years. They were also briefly
tested with an infrared pupilometer for a normal pupil response to
changes in light level and were rejected if that was not the case.
Those chosen were essentially naive with no special knowledge of
lighting and were unaware of the study purpose. A total of 57
subjects were tested. The distribution of these subjects is divided
between three age groups as follows: [0116] Age 18-30: 19 subjects
[0117] Age 31-50: 21 subjects [0118] Age 51 & over: 17
subjects
[0119] The analysis of these subjects required that they completed
testing for all conditions for each of the tests, 1) Brightness
Comparison (BC);2) Pupil Size (PS); and 3) Brightness Matching(BM),
the latter being a separate study described in a separate paper.
Due to some equipment errors in reading lighting measurements
and/or obtaining pupil size data, the total number of subjects
analyzed for each test varies. The total number of subjects
analyzed for each test, by age group, and based on having complete
data is as follows in
TABLE-US-00005 TABLE 3 Table 3: Summary of Subjects in final
analysis, by age group TEST 1: Brightness Comparison (BC) Study:
Subject Age Group BC Test PS Test BM Test Age 18-30 17 14 16 Age
31-50 16 13 12 Age 51 & over 14 13 12 TOTAL No. of 47 40 40
[0120] General:
[0121] For this study, all nine conditions shown in Table 2 were
tested. All four metameric pairs were tested at 60 and 150 DOG lux,
and one metameric pair (Pair 2) was examined at a much higher level
of 400 Lux. The purpose of this latter test was to examine
comparisons at a sufficiently high illuminance level where
similarity of results would reasonably assure the absence of
possible rod receptor effects. The comparisons were portioned by
light level into these three illuminance categories. The 4 metamer
comparisons in the 60 and 150 Lux conditions were presented in
randomized order between subjects in each illuminance category.
Subjects were informed that the lighting would be switched back and
forth between 2 scenes and they would be asked to indicate which of
the 2 scenes appeared brighter.
[0122] Protocol:
[0123] Each subject was adapted to the first condition in each of
the categories for a period of 2 minutes focusing on the iPad mini.
Subsequently the two viewed scenes are alternated with the viewing
time for each scene totaling the sum of the Transition Interval of
1 second and an Observation/Decision Interval of 5 seconds for a
total time of 6 seconds. Each time the scene was presented, the
experimenter called out the scene as "A" or "B", and after 3
repetitions of each pair, the experimenter asked the subject to
report which one is brighter recording the subject's decision in
the computer. Subjects were not allowed the choice of "No
Difference". This resulted in an approximate total time for a given
subject for each pair as 6 seconds x 6 presentations) +a few
seconds decision time totaling about 1 minute.
[0124] Light measurements for each subject were made during the
initial 2-minute adaptation period (condition A), and then once
again during the 3.sup.rd presentation of condition B, just before
the subject made their final decision. The decision was recorded as
`A` or `B`. The experimenter was not informed of which metamer was
being presented during any of the tests other than the names `A` or
`B`.
TEST 3: Pupil Size Determinations:
[0125] General:
[0126] Since it had already been established that melanopsin
stimulation is a significant factor in controlling pupil size
[McDougal &Gamlin (2010), Vienot (2010), Tsujimura (2010)] it
was reasonable to expect that there could be pupil size differences
associated with the different metamers. The earlier studies on
brightness perception mentioned above did not measure pupil size as
a companion to the brightness perceptions but did show that
lighting spectra with higher S/P (or melanopsin content) were
perceived as brighter. By present understanding these brightness
perceptions would be associated with smaller pupils and therefore
less retinal illuminance, but nevertheless perceived as brighter.
Thus, in order to fulfill the original study objectives, potential
pupil size differences were examined. This was accomplished by
employing an ISCAN infrared pupilometer.
[0127] Protocol:
[0128] In order to shorten the subject time and to answer the
question of associated pupil size differences it was deemed
sufficient to examine pupil responses at the 150 Lux condition with
the following 4 comparisons.
[0129] Pair 2, Low S/P, 150 Lux
[0130] Pair 2, High S/P, 150 Lux
[0131] Pair 1, Low S/P, 150 Lux
[0132] Pair 1, High S/P, 150 Lux
[0133] The following protocol was followed for each of the lighting
conditions tested:
[0134] A 3-minute adaptation time was provided for each metamer
prior to recording pupil diameter data. The subject was then
instructed to maintain his/her gaze at the iPad. The experimenter
also recorded the light measurements from the Gigahertz light meter
during this adaptation time. After adaptation time was completed,
pupil diameter data was recorded for 30 seconds. The experimenter
then switched the lighting to the next lighting condition and
repeated the process.
[0135] When these 4 tests were completed the experimenter closed
the session. The data collected for later analysis of pupil size
behavior consisted of a continuous 10-second blink free sample from
each 30-second pupilometer readings.
Results:
[0136] Data Output and Analysis:
[0137] Two computer data files were produced for each subject, one
which was custom-programmed software that captured the data from
the Gigahertz light meter for all steps of the testing, and the
other that captured the pupilometry data from the ISCAN
pupilometer. Both files for each subject provided output in a
standard format such that a third independently written Subject
File program for data collation was developed, which imported each
of these two files and provided a summary of the data in a more
usable format.
[0138] The data for each subject was scrutinized to determine if
any of the recorded light levels or S/P values were out-of-bounds
relative to the constant values in Table 2 for the BC and also for
the follow-on BM tests. The Subject File also automatically
determined if there was a valid 10-second section of pupilometry
for each subject. This data inspection provided the necessary step
to determine what, if any, data could not be used on account of
unanticipated lighting changes that occurred during the test.
Furthermore, if the recorded light measurements were some value
that was not consistent with the test parameters, those results
could not be attributed to the test conditions and thus that data
was considered unreliable and not usable.
[0139] The results of the data analysis concluded that occasionally
there were some failures of equipment or a light level was not
recorded resulting in incomplete or not verifiable data. The
following criteria were adopted as a pre-condition for excluding
that data.
[0140] Exclusions for the BC test: [0141] Either preset A or B
inadvertently records a zero illuminance value [0142] Preset A or B
was significantly different than the reference light level (60, 150
or 400 lux) [0143] Any measured S/P value differed from the
programmed value by 0.05 or greater. [0144] Exclusions for
Pupilometry: [0145] Pupilometry data is excluded for those cases
where BC and BM data is excluded. [0146] The measured light level
and/or S/P value was significantly different than the correlating
measured light levels employed for the follow-on BM measured
values. [0147] A continuous 10 second blink free period of
pupilometer data could not be found.
[0148] The result of applying these exclusions provided valid data
for 47 subjects for the BC tests and 40 subjects for the
pupilometry measurements.
[0149] Brightness Comparison Summary:
[0150] The dependent variable in the brightness comparison study is
the frequency with which the higher S/P source was chosen as
brighter in comparison with the lower S/P source. There were a
total of 423 runs, spread over the 9 conditions shown in table 2,
and over 3 age groups: 18-30, 31-50 and 51 and older. The number of
subjects in each age group was 17, 16 and 14 respectively. The
results can be analyzed in terms of the entire population, and as a
function of the ratio of the S/P ratios, the illuminance at the
eye, and the age of the subjects.
[0151] The test over all conditions confirmed that there is an
effect of the S/P ratio difference. The higher S/P source was
perceived as the brighter source in 375 of the 423 runs. The
unbiased estimate of the probability is 88.5%.+-.1.5% (n=#
brighter, N=total # of runs, mean=(n+1)/(N+2), SE=
[n+1)(N+1-n)/(N+2)(N+3) 2]). The probability that the true mean is
50% is on the order of 10.sup.-135, so the main hypothesis that the
S/P ratio affects brightness is confirmed in this study.
[0152] The results were highly significant for all age groups and
somewhat unexpectedly the oldest group had a somewhat higher
percentage in favor of the higher S/P spectrum. As mentioned,
testing was also performed at a high value of 400 vertical Lux
where similar results were obtained lending assurance to the
conclusion that the measured effects were unlikely due to possible
rod receptor transients. The summary of results is listed in Table
4.
[0153] The variability of both S/P and illuminance over the various
subject runs was very low. The maximum variation in S/P within a
run was 5%, and the standard deviation of the S/P values for the
runs averaged 1%. These variations are small relative to the
differences in S/P between sources.
[0154] The maximum variation of the illuminances was under 4%. The
average DOG illuminance for the low S/P source in each run was 0.3%
higher than that of the higher S/P source. The higher S/P source
had a higher photopic illuminance in only 21% of the runs, and the
worst-case excess was only 1.9% (1.1 lux at 59 lux). These results
are in the opposite direction of the hypothesis, and therefore do
not represent the presence of a confounding condition.
TABLE-US-00006 TABLE 4 Summary results from the Brightness
Comparison (BC) Test. Brightness Comparison Results for 47 Subjects
Summary Findings % of Subjects [selecting] higher S/P lighting as
brighter BC Test High S/P 3.069 3.039 3.041 2.086 2.064 3.938 3.938
2.599 2.582 Low S/P 2.134 2.117 2.111 1.346 1.352 2.077 2.058 1.217
1.233 Delta 0.935 0.922 0.930 0.740 0.712 1.861 1.880 1.382 1.348
S/P Avg Age Across LS- HW- HW- LW- Group Qty Tests HS-60 HS-150
HS-450 LS-60 150 60 150 60 LW-150 18-30 17 84% 65% 76% 82% 88% 94%
76% 88% 88% 94% 31-50 16 91% 81% 81% 88% 94% 100% 94% 94% 88% 100%
51- 14 92% 86% 93% 93% 93% 93% 79% 93% 100% 100% Older Total 47 89%
76.6% 83.0% 87.2% 91.5% 95.7% 83.0% 91.5% 91.5% 97.9% Ave for both
light levels 79.8% 93.6% 87.2% 94.7%
[0155] Because of the methodology used to construct the metamers
for the low and high CCT values it was not possible to perform
unbiased estimation of the effect of CCT in the brightness
comparisons.
Pupil Size Results Summary:
[0156] Pupil sizes were successfully measured for 40 of the 47
subjects that completed the BC tests for the 4 conditions at 150
Lux. For the wide spread in S/P values (ratio H/L=1.91) 37 of the
40 subjects showed smaller pupils for the higher S/P value and for
the small spread (S/P=1.44) 32 subjects showed smaller pupils for
the higher S/P value. On average these results confirm those of
other pupil size measurements Berman et al (1992), MacDougal &
Gamlin (2010), Tsujimura et al (2010), Vienot (2010) and further
demonstrate that pupil size is affected by the S/P or melanopic
content of the viewed spectrum. These results also show that even
though the photopic retinal illuminance is lower for the higher S/P
spectrum (because of the smaller pupil size) the higher S/P
spectrum is perceived as brighter.
[0157] Discussion:
[0158] For the conditions of the simulated athletic field with
approximately 1/4 of the complete visual field lit, reliable data
from 47 subjects of ages ranging from 18 years to 60 years clearly
showed a very significant and unequivocal effect on perceived
brightness. They had a total of 423 opportunities to compare
whitish metameric lightings of different spectral content and chose
the spectra of higher S/P (or higher melanopic) content to be
perceived as brighter 88% of the time even though the photopic
illuminance at the eye was unchanged. The metamerism provided by
the use of the Stockman-Sharpe cone spectral sensitivities along
with the application of the Cohen & Kappauf methodology allowed
for the construction of many whitish metamers with nearly
undetectable color differences by most subjects. In this manner,
the possibility of color confounds in the comparisons that might
have occurred in other studies such as Royer &Houser (2012),
especially when the difference in S/P values is small, have been
greatly reduced.
[0159] Our results clearly demonstrate that for whitish lighting
and when the lit field of view is extra-foveal, photopic
illuminance is not the unique predictor of perceived brightness and
that spectral content as described by the S/P value is also a
necessary descriptor. Furthermore, these results obtained under the
modified conditions here, both compliment and extend the earlier
results of Berman et al (1990) and Brown et al (2012). To the
extent that the metamerism employed here is accurate, the
comparisons evaluated are based on identical cone stimulation and
thus the judgment differences cannot be associated with the
predominance of any single cone receptor response such as an S-
cone effect.
[0160] Presumably the underlying mechanism for the brightness
perceptions is the result of the action of the retinal melanopsin
receptors (Hattar et al 2002) whose spectral behavior when
stimulated by polychromatic light sources is highly correlated with
the ratio of scotopic to photopic S/P content of those sources
[Berman (2008), Berman & Clear (2008,2014)] thus allowing the
S/P value as a marker of melanopic content. This high degree of
correlation is shown in FIG. 10I below taken from Berman &
Clear (2014). FIG. 10I relates to the following: Melanopic/lumen vs
S/P Correlation: This graph shows the correlation between melanopic
sensitivity and S/P value based on the spectral power distributions
of a sample of 60 "white" light sources, and 28 color sources such
as monitor colors. The S/P ratios of the whites ranged from 0.81 (a
low color temperature high pressure mercury) to 2.62 (7500.degree.
K. fluorescent lamp), while the S/P ratios for colors ranged from
0.23 (low pressure sodium) to 10.6 (LED monitor color blue). The
fitted equation with a 99.4% correlation is given by Melanopic
mw/photopic lumen (Mmw/P)=(0.041212*S/P+0.45827)*S/P -0.07 428
Range: 10. 7>SIP >0.22. Melanopic content is based on the
melanopic sensitivity function, Lucas et al (2014), and given in
the Tool Kit website.
[0161] The perceived brightness differences of this study are
observed in a very short exposure time of a few seconds thereby
reducing the dependence on memory load. Because of the switching
protocol employed and the vagaries of memory, any accurate
estimation of the longtime stability of these brightness
perceptions is essentially precluded. If melanopsin receptors are
the underlying mechanism Do et al (2010) then the action time of
the stimulating retinal pathways would be much shorter than the
time course associated with the post illumination pupil response
(PIPR) claimed as elucidating the typical response time for
melanopsin receptors (McDougal& Gamlin, 2010). To the extent
that our metamers are veridical and that rod receptors are not the
underlying mechanism, our results indicate the likelihood of a
rapid melanopic related response Peirson et al (2009).
[0162] The potential practical and economic consequences for
lighting engineering that relate to the magnitude of this
brightness effect are evaluated in the follow-on study of
brightness matching.
REFERENCES:
[0163] Bailes H J, Lucas R J. (2010). Melanopsin and inner retinal
photoreception. Cellular and Molecular Life Sciences, 67(1),
99-111. [0164] Berman S M, Jewett D L, Fein G, Saika G, Ashford F.
(1990), Photopic luminance does not always predict perceived room
brightness. Lighting Research and Technology 1990; 22: 37-41.
[0165] Berman, S. M., G. Fein, D. L. Jewett, G. Saika, and F.
Ashford (1992). Spectral Determinants of Steady-State Pupil Size
with Full Field of View. Journal of the Illuminating Engineering
Society, 21(2) 3-13. [0166] Berman, S M &Clear, R D; 2008; Past
vision studies can support a novel human photoreceptor, Light &
EngineeringVol. 16, No. 2, pp. 88-94. [0167] Berman, S. M; 2008, A
new retinal photoreceptor should affect lighting practice Lighting
Research and Technology; 40; 373. [0168] Berman, S M & Clear, R
D (2014) Implications of the Relationship between S/P and Melanopic
Efficiency: Illum Eng. Soc Conference report Nov. 2014 [0169]
Boynton R M. (1996) J Opt Soc Am A Opt Image Sci Vis.
Aug;13(8):1609-21. Frederic Ives Medal paper. History and current
status of a physiologically based system of photometry and
colorimetry. [0170] Brown T M, et al. (2012) Melanopsin-based
brightness discrimination in mice and humans. CurrBiol
22(12):1134-1141. [0171] CIE (2006) Fundamental chromaticity
diagram with physiological axes--Part 1 Technical Report 170-1.
[0172] Cohen, J B and Kappauf, W E, (1982) Metameric color stimuli,
fundamental metamers, and Wyszecki's metameric blacks. The American
Journal of Psychology 95(4):537-64. [0173] Cohen, J B and Kappauf,
W E (1985), "Color mixture and fundamental metamers: Theory,
algebra, geometry, application", American Journal of Psychology.
1985 Vol. 98, No 2, pp. 171-259. [0174] Do M T, Yau K W (2010)
Intrinsically photosensitive retinal ganglion cells. Physiol Rev
90(4):1547-1581. [0175] Ecker J L, et al. (2010)
Melanopsin-expressing retinal ganglion-cell photoreceptors:
Cellular diversity and role in pattern vision. Neuron 67(1):49-60.
[0176] Harrington, R. E. (1954). Effect of color temperature on
apparent brightness. J. Opt. Soc [0177] Hattar S, et al (2002)
Melanopsin-containing retinal ganglion cells: Architecture,
projections, and intrinsic photosensitivity. Science
295(5557):1065-1070. [0178] Lucas, R., Lall, G., Allen, A. &
Brown, T (2012). How rod, cone, and melanopsin photoreceptors come
together to enlighten the mammalian circadian clock. Prog Brain
Res, 199, 1-18. [0179] Lucas R J, Peirson S N, Berson D M, Brown T
M, Cooper H M, Czeisler C A, Figueiro M G, Gamlin P D, Lockley S W,
O'Hagan J B, Price LLA, Provencio I, Skene D J, Brainard G C (2014)
Measuring and using light in the melanopsin age. Trends in
Neurosciences 37:1-9. [0180] McDougal, D. H. & Gamlin, P. D.
2010 The influence of intrinsically-photosensitive retinal ganglion
cells on the spectral sensitivity and response dynamics of the
human pupillary light reflex. Vision Res. 50, 72-87. [0181] Peirson
S N, Halford S, Foster R G (2009) The evolution of irradiance
detection: Melanopsin and the non-visual opsins. Philos Trans R Soc
Lond B BiolSci 364(1531): 2849-2865. [0182] Royer M P & Houser
K W, (2012) Spatial Brightness Perception of Trichromatic Stimuli:
LeukosVol 9, No2, (Oct)pp.8 9-1 0 8 [0183] Shaw, Mark Q, (1999),
Evaluating the 1931 CIE Color Matching Functions: A thesis
submitted in partial fulfillment of the requirements for the degree
of Master of Science in Color Science in the Center of Imaging
Science, Rochester Institute of Technology June 1999 [0184]
Stockman, A., & Sharpe, L. T. (1999). Cone spectral
sensitivities and color matching. In K. Gegenfurtner& L. T.
Sharpe (Eds.), Color vision: From Genes to Perception (pp. 53-87)
Cambridge: Cambridge University Press. [0185] Stockman, A. and
Sharpe, L. T. (2000) Spectral sensitivities of the middle-and
long-wavelength sensitive cones derived from measurements in
observers of known genotype. Vision Research, 40, 1711-1737. [0186]
Stockman, A., & Sharpe, L. T. (2006). Physiologically-based
colour matching functions. In Proceedings of the ISCC/CIE Expert
Symposium `06: 75 Years of the CIE Standard Colorimetric Observer
(pp. 13-20). Vienna: CIE Central Bureau.
[0187] Tool Kit: [0188]
http://lucasgroup.labls.manchester.ac.uk/research/measuringmelanopicil
luminance/Tsujimura S, et al (2010) Contribution of human
melanopsin retinal ganglion cells to steady-state pupil responses.
Proc BiolSci 277 (1693):2485-2492. [0189] Vienot, F. (2010) The
effect of controlled photopigment excitations on pupil aperture.
Ophthal Physiol. Opt 30: 484-491. [0190] Vienot, F et al., (2012)
"Domain of metamers exciting intrinsically photosensitive retinal
ganglion cells (ipRGCs) and rods", Journal of Optical Society of
America A, Feb. 2012, Vol 29, No 2, pp. A366-A376.
[0191] E. IES#2 (Supplemental Information)
[0192] Brightness matching determines the trade-off between S/P
values and illuminance level.
[0193] Bradley Schlesselman, Myron Gordin, Larry Boxler.sup.1,
Jason Schutz, Sam Berman.sup.2, Brian Liebel.sup.2, Robert
Clear.sup.2
[0194] Musco Sports Lighting, LLC, 100 1.sup.st Avenue West,
Oskaloosa, Iowa 52577
[0195] Abstract:
[0196] In a previous Brightness Comparison study (BC Study,
Schlesselman et al 2015), brightness perception comparisons in a
simulated sports field were evaluated for photopically equal and
constant color lighting (metamers) but of different melanopic
content, as measured by the S/P ratio. In that study, subjects
overwhelmingly judged the lighting with the higher S/P value as
appearing brighter. In this companion study, 40 subjects who
completed the previous study comprising the 3 age groups (18-30
years, 31-50 yrs and >50 years) sat in a chair positioned at an
edge and midpoint of the simulated field, providing a binocular and
unobstructed view of both the lit "field" and dark surround that
simulates a real sports field. The subjects were provided with a
means to adjust light levels to achieve an equality of perceived
brightness. The illuminance levels were 60 and 150 vertical lux at
eye level in the direction of gaze, corresponding to those measured
for spectators and performers in an operating field. Subjects were
Musco employees or their family that had no special knowledge in
lighting and were unaware of the study purpose. The lighting
utilized theatrical luminaires with multiple and different colored
LED sources combined to form four pairs of metamers, each pair
consisting of one metamer having a relatively higher S/P ratio
compared to the other. Two pairs had relatively higher nominal CCT
values than the other two pairs, and within each CCT set of
metamers, one pair had a wide spread between the high and low S/P
ratio metamer, while the other pair had a relatively smaller
difference between the S/P ratios. The S/P values ranged
approximately from 1.2 to 4 and the difference between the S/P
values for a compared pair varied between 0.72 and 1.86.
[0197] The conventional CCT values ranged from nominal 2700K to
6700K. In order to achieve a condition of equal brightness
perception, subjects were given repeated opportunities to adjust
the level of one of the lighting conditions within a given
metameric pair (randomly selected as the high S/P or low S/P
source) by raising or lowering the light level with a manual
dimming control slider to select a level where the 2 lightings
appeared equally bright. This test was performed at two light
levels (60 &150 Lux) for each of the four metameric pairs. In
this test, 92% of the 40 subjects chose to lower the photopic level
of the higher S/P lighting to obtain an equality of brightness
perception. Overall, the high S/P source was set to a lower light
level than the low S/P source 293 times out of 320 runs, which has
a probability of 10.sup.-151 of occurring by chance.
[0198] The amount of light level reduction was determined leading
to an augmentation of the dependence of brightness perception on
photopic illuminance P by the factor P(S/P).sup.n The exponent n
was empirically determined from the data as n=0.436.+-.0.017.
[0199] The role of conventional CCT within each metameric pair was
also examined and it was shown that there was no statistically
significant effect. In terms of practical applications for lighting
engineering, these results show that substantial energy savings can
be achieved by replacing sources with relatively low S/P values
with e.g. LED sources capable of higher S/P values while
maintaining the same brightness perception even in a nighttime
environment where only a fraction of the visual field is lighted.
For example, replacement in a lighted athletic field employing a
typical MH source of S/P=1.4 by a LED source of S/P=2.4 would lead
to the possibility of a 25% light level reduction based on the
principle of equal perceived brightness. This feature is of
sufficient magnitude that it should be a design consideration for
sports lighting applications.
[0200] Background:
[0201] Previous studies Berman et al (1990), Brown et al (2012),
Royer &Houser (2012) have shown that in conditions of full
field of view lightings of the same color but of different spectral
content and also with equal photopic luminance (metamers) are not
perceived as equally bright. Current understanding of these
observations [Brown et al (2012), Ecker et al, (2010), Lucas et al
2014] is that they are likely a result of the responses of
non-image forming melanopsin photoreceptor widely distributed in
the retina of the eye and whose spectral responses are not included
in the determination of photopic luminance. Thus, it is reasonable
to expect that there could be a trade-off between melanopic content
and photopic light level to achieve a given level of brightness
perception. The quantitative aspect of this trade-off was not
examined in the previous studies and as such is the primary
objective of the present study.
[0202] Methods:
[0203] The testing took place in the same room as the BC study of
brightness comparisons (Schlesselman et al 2015). The simulated
sports field was constructed inside a large hall and had the
dimensions of 30 by 20 feet (width and length). To simulate a
realistic sports lighting situation, it was lit so that about 3/4
of the visual solid angle was in the dark from the perspective of
the subject situated at the midpoint of the longer dimension and at
the front end of the shorter dimension. FIGS. 10A, 10B and 10C show
a perspective view of the simulated field construction, a
cross-sectional drawing, and a photograph, respectively, of the
test environment. The simulation of the field was accomplished by
lighting only the lit portion of the test floor, which was painted
a spectrally neutral matte gray color and had an incline of 7.5
degrees to establish concordance in the end point viewing angle of
the subject as would occur on the real field. The dark portion was
obtained by using matt black fabric that was placed to surround the
lit portion of the test space.
[0204] Achieving the necessary illuminance at the subject's eye
required both direct lighting on the test field floor plane to
yield a field luminance distribution approximating that of the real
sports field, along with the addition of several overhead fixtures
that provided the majority of vertical illuminance at the observer
eye that would come from typical high mast sports lighting
luminaires in real conditions. Attention was paid to assure that
these overhead fixtures were not directly visible by the subject as
well as to minimizing possible direct glare due to the proximity of
these overhead fixtures in relation to the subject position (see
FIG. 10D).
[0205] For the study, subjects sat in a chair at the midpoint of
the long dimension at the edge of the lit floor as seen in FIG. 10C
and viewed an iPad Mini tablet placed in line with center of the
long dimension and at the middle of the lit floor. The iPad screen
subtended essentially a foveal visual angle of about 3 degrees from
the subject position and provided a fixation point. The iPad was
set to display slow temporal screen variations by showing a
simulated lava lamp scene of fixed color thereby helping to reduce
boredom and to assure that the direction of gaze would be similar
for all subjects. The iPad was placed in the center of a 12 inch
diameter black circle (FIGS. 10C and 10D) and together these
essentially foveal objects help to minimize the transient `Maxwell
Spots` that can be sensed in the central visual field when
switching between test metamers and when the lit field of view
extends much beyond the fovea.
[0206] The lighting system and the construction of the metamers are
the same as in our previous study (Schlesselman et al 2015) and are
described in detail there. As in our previous study achieving equal
color of the compared lightings is obtained by assuring equal
excitation of the 3 retinal cones accomplished through employing
the Stockman cone fundamentals (Stockman et al 1999.2000,2006, CIE
2006) and not by equality of the CIE tristimulus values. Metamers
are constructed using the methods described by Cohen & Kappauf
(1982,1985) and Vienot et al (2012)
[0207] The same 7 LED sources and 4 metameric pairs as employed in
the previous study are also used for this study. The CIE
chromaticity values of these metamers are shown graphically in FIG.
10F below along with their spectral power distributions in FIG.
10H.
TABLE-US-00007 TABLE 5 Lighting Conditions: Vertical DOG
Illuminance, S/P values and CCT values. Illuminance Levels
Illuminance Levels 60 150 400 60 150 400 Pair Description Code S/P
S/P S/P CCT CCT CCT 1 High CCT HWH 3.952 3.898 5653 5475 Wide S/P
HWL 2.088 2.064 6580 6380 Spread Delta 1.864 1.834 -927 -905 2 High
CCT HSH 3.087 3.009 2.937 6444 6224 5992 Small S/P HSL 2.145 2.128
2.117 6706 6588 6434 Spread Delta 0.942 0.881 0.820 -262 -364 -442
3 Low CCT LWH 2.610 2.599 2389 2373 Wide S/P LWL 1.222 1.239 3109
3149 Spread Delta 1.388 1.36 714 -776 4 Low CCT LSH 2.098 2.073
2713 2688 Small S/P LSL 1.352 1.356 3040 3054 Spread Delta 0.746
0.717 -327 -366
[0208] Lighting Measurements:
[0209] Throughout the testing procedure, lighting measurements were
taken to ensure that light level and color consistency was
maintained for each test. The light meter (Gigahertz Model#
BTS256-E BiTec Sensor Luxmeter) also recorded the final light level
reading for the matched brightness condition and provided the
necessary readings to ensure that color consistency was maintained
while the light sources were being dimmed. The meter was a
positioned to measure the vertical illumination at the eye in the
Direction of Gaze (DOG illuminance), as well as the Spectral Power
Distribution curves received at the eye. The S/P value was
calculated from the measured SPD for each lighting measurement
taken. The same meter provided output data into a computer file
that recorded the measurements for all tests, and these
measurements were reviewed for each subject and for each test.
[0210] Subjects:
[0211] The same subjects as those who participated in the previous
Brightness Comparison study participated in the brightness
matching.
[0212] A total of 40 subjects completed the brightness matching
with 16 in the younger than 30 years, and 12 each in the other 2
age groups.
[0213] Brightness Matching
[0214] Protocols: General:
[0215] Employing the same set of lighting conditions as in the BC
study, subjects were given a manual slider control whose purpose
was to adjust the light level of the `B` condition to match the
fixed `A` lighting condition of the BC testing. Subjects were
instructed to adjust the slider so that the 2 scenes would appear
equally bright.
[0216] Specific Protocol:
[0217] To implement the matching the experimenter instructed the
subject to move the slider to adjust light intensity of Scene B to
match the brightness of Scene A (fixed) until the subject judged
the two scenes to be equal in brightness. The scene of fixed
illuminance was randomly chosen as either the high or low S/P
condition. The subject was allowed to ask the experimenter to
switch back and forth between scenes in order that they can further
adjust the light level as many times as they wanted. Subjects were
told to try to judge equivalency in a short time period following
switching (close to 1 second, no longer than 5 seconds). After
achieving equivalent brightness, the experimenter presents each
scene for 5 seconds to confirm the equal brightness setting with
the subject. The subject was allowed final tweaking if they change
their mind after viewing the conditions under a longer exposure.
The experimenter recorded the resulting DOG illuminance equivalency
level with appropriate button push.
[0218] This process was repeated for each of the seven remaining
pairs, with a 30 second adaptation time between each new pair
within the light level, a five minute break between the light level
changes from 60 to 150 Lux (between test 4 and 5). The subject time
to accomplish this was approximately 30 minutes at most. Light
measurements were recorded for each subject and for each
condition.
[0219] Brightness Matching (BM) Results:
[0220] This test employed the same set of conditions as for the BC
testing except the 400 Lux condition was not used due to the
limitations of the light sources. Thus, there were 8 different
conditions (4 at 60 Lux and 4 at 150 Lux) as shown in Table 5
above. Thirty-nine of the 40 subjects were the same as those that
participated in the BC study and the one additional subject was an
excluded subject in the BC testing because of a failure to record
the light levels.
[0221] Not all subjects chose a lower illuminance for the higher
S/P source, and this reversal was more pronounced when the
difference in S/P ratios between the two metamers were close.
However, even in the worst cases (HS-60 and HS-150), 33 out 40
subjects used a lower illuminance for the high S/P source. The
probability of this occurring by chance is 0.002%. For the wide
spread in S/P values the worst case was 37 out of 40 and the best
case was 40 out of 40. Thus, there was a clear indication that the
higher S/P sources required less illuminance to achieve the
perceived brightness of the lower S/P sources. The summary of
results is given below in Table 6.
TABLE-US-00008 TABLE 6 Summary results from the Brightness Matching
(BM) Test. Brightness Matching Results for 40 Subjects Summary
Findings % of Subjects selecting lower illuminance for high S/P
lighting BM Test High S/P 3.078 3.044 2.087 2.064 3.938 3.938 2.599
2.582 Low S/P 2.133 2.117 1.347 1.352 2.077 2.058 1.217 1.233 Delta
0.945 0.927 0.740 0.712 1.861 1.880 1.382 1.348 S/P Avg Age Across
HS- LS- HW- HW- LW- Group Qty Tests HS-60 150 LS-60 150 60 150 60
LW-150 18-30 16 87% 69% 63% 88% 88% 94% 94% 100% 100% 31-50 12 83%
83% 92% 100% 92% 83% 92% 100% 100% 51- 12 97% 100% 100% 83% 100%
100% 100% 92% 100% Older Total 40 92% 82.5% 82.5% 90.0% 92.5% 92.5%
95.0% 97.5% 100.0% Ave for both light levels 79.8% 93.6% 87.2%
94.7% Ave. Light Level Reduction (% Using Low S/P as base) Ave.
Reduction 14.3% 11.7% 13.6% 15.1% 20.7% 25.1% 27.3% 27.9%
Percentage (Using Low S/P as base) Ave for both light levels 13.0%
14.3% 22.9% 27.6%
[0222] Statistical Analysis of Brightness Matching Study:
[0223] Forty subjects adjusted the brightness of a test light to
match the brightness of a reference light. The lights were
metameric in color, but differed in their S/P ratios. Each subject
did 8 matches covering 2 reference illuminance levels at the eye;
60 and 150 lux, and 4 different sets of S/P ratios. An attempt was
made to extend the illuminance range to 400 lux, but the apparatus
did not have a sufficient illuminance range to allow brightness
matches for all subjects, so this attempt was aborted, and the
4001ux data was dropped from further analysis. The subjects were
grouped into age groups as in the study of brightness comparison,
with the number in the age groups being 16, 12, and 12,
respectively.
[0224] The average ratio of S/P values over the two sources for the
eight runs ranged from 1.44 to 2.13. The maximum deviation from the
average ratio within a run was two percent. The dependent variable
in the brightness matching experiment i.e. the ratio of photopic
illuminances for equal brightness perception, is a continuous
variable, and is amenable to least squares fitting. We found that
the fit to S/P ratios explains more of the variance than a fit to
CCT (as computed in the standard XYZ space), and is therefore the
preferred explanation for the results. We lastly show that there
appears to be no interaction between S/P and CCT in these metameric
matches.
[0225] The BC Study (Schlesselman, 2015) showed that subjects chose
the high S/P source as being brighter than the low S/P of the same
illuminance at the eye at a statistically significant level. In
this Brightness Matching (BM) test this should translate into
subjects choosing a lower illuminance at the eye for the high S/P
source than for the low S/P source. With 8 runs for each subject,
32 of the 40 subjects chose a lower illuminance for the high S/P
source than the low S/P source at a statistically significant level
(7 out of 8 runs). Only one subject showed no preference (4/8).
When averaged over subjects, the worst cases were for the two runs
where the S/P ratio for the high to low S/P source was 1.44. Even
for these two runs, 33 out of 40 subjects had a positive result
(P=0.002%). Overall, the high S/P source was set to a lower light
level than the low S/P source 293 times out of 320 runs, which has
a probability of 10.sup.-151 of happening if the true probability
was 50%.
[0226] Thirty-nine of the 40 subjects in the brightness matching
study also had complete data for the BC study with the same sets of
reference conditions. A comparison of the two studies highlights
the variability of the results in the BC study. Of the 312 matching
runs in the BC study, 26 of them had a negative result in that the
low S/P source was judged brighter than the high S/P source. In the
equivalent brightness matching experiment, only 9 of these
conditions resulted in a negative result brightness match requiring
a higher lux level with the high S/P source. The BC results did
predict a difference in the average brightness matching
illuminances. The 26 conditions with a negative brightness
comparison had an average illuminance ratio of the low S/P source
to the high S/P source of 1.036 (which is a slightly positive
result). The 286 runs with a positive brightness comparison had an
illuminance ratio of 1.29 on the brightness match, which is a
strongly positive result.
[0227] A Model for Brightness Perception:
[0228] The main point of the BM study, other than demonstrating
that there was an effect, was to identify the S/P exponent in the
simple model of brightness dependence, i.e.,
logB=const.times.log[P(S/P).sup.n]=const.times.log B.sub.br
[0229] where the "brightness lumen", B.sub.br, has the simple form:
B.sub.br=P.times.(S/P).sup.n.
[0230] In the BM study, the brightness of the reference source, B1,
is adjusted to achieve equal brightness of the test source, B2. If
we let r=S/P, then the log of the ratio of the illuminances is
equal to a constant, n, times the log of the ratio of the S/P
ratios: log(P.sub.1/P.sub.2)=nlog(r.sub.1/r.sub.2). A least-squares
fit for n gives the value n=0.436.+-.0.017.
[0231] This result is the principal quantitative determination for
the BM testing.
[0232] The exponent is slightly smaller but reasonably close to
that determined in the earlier study of Berman et al (1990) carried
out in conditions where the full field of view was illuminated and
where the exponent was determined there roughly as 0.5.
[0233] The age of the subject was close to significant in the BC
study. We tested for an interaction of age and brightness exponent.
Although the trend of the younger subjects appearing to have a
lower exponent, the result was not statistically significant at the
P=30% level. However, a similar test for the interaction of subject
and exponent was significant at the P <0.01% level. Adding a
subject interaction term increases the amount of variance explained
by the fit from 17% to 47%, and slightly reduces the standard error
of the exponent to 0.015. Subject exponents ranged from 0.061 to
0.0.922, and had a standard deviation about the mean of 0.185. Note
the standard deviation appears to reflect a real variation in
sensitivity to the S/P ratio among subjects.
[0234] The S/P value was also statistically significant in the BC
study, but much of this effect should be caught in the analysis of
the data in terms of the S/P exponent. The illuminance level was
not a statistically significant effect in the brightness comparison
study. Both factors are rejected in the analysis of exponent for
the BM study.
[0235] Is there an effect of CCT?
[0236] We examined the possibility of there being an interaction
between S/P and color temperature by looking for a difference in
the calculated S/P exponent in the high CCT versus the low CCT
tests. A within subject comparison matching the illuminances, and
the rough S/P ratios gave 160 differences between the high and low
CCT runs. The difference of high--low CCT was 0.013.+-.0.034, which
is not statistically significant. We therefore rejected the
hypothesis that there was an interaction between CCT and S/P in the
perception of brightness in these metameric matches and conclude
that there was no significant effect of CCT in the brightness
matching study.
[0237] Limen Test: (Testing Subject Discerning Ability to Match
Brightness) Description:
[0238] The purpose of the limen test was 2-fold; the first is as a
check that the equipment is functioning properly and second to
evaluate the discerning ability level of the group of 40 subjects
that successfully completed the BM test. That is, how good they are
at being able to state that one condition can be adjusted to appear
as having an equal brightness. To assess this ability to match
alternating scenes for equality in brightness perception the limen
test was performed. In this case the lighting for the 2 alternating
scenes had equal spectral content with a nominal S/P value of 2.12
but where a test lighting of different DOG illuminance was to be
adjusted by the subject with the slider so as to appear equally
bright when compared with a standard scene of fixed illuminance.
For the initial condition the test lighting was either 20% higher
or 20% lower than the standard scene and alternated between
successive subjects. Subjects then adjusted the test illuminance
level with the slider until there was a match in brightness
perception. The testing was done at the 2 standard levels of 60 and
150 Lux.
[0239] The detailed protocol was essentially the same as in the BM
testing and is as follows. The subject was instructed to focus on
the iPad Mini and allowed adaptation to the light condition scene
A, which was the baseline illuminance, for 2 minutes for each of
the 2 standard levels. After this period was complete, the
experimenter alternated between scenes A and B, with the subject
using the slider dimmer to adjust scene B to the level they felt
was equal to scene A. Scene Blight level was set at an increase or
decrease of 20% and with the increased or decreased value
alternating with each successive subject.
[0240] The subject could ask the experimenter to switch back and
forth between scene A (fixed light level) and scene B (adjustable
light level), with the reminder that the subject should try to
judge equivalency in a short time period following switching (close
to 1 second, no longer than 5 seconds).
[0241] After achieving equal brightness perception, the
experimenter presented each scene for 5 seconds and confirmed the
equal brightness setting with the subject. The subject was allowed
final tweaking if a final change was desired after viewing the
conditions under the longer exposure. The experimenter then
recorded the resulting equivalency light level with an appropriate
button push.
[0242] Limen Test Results:
[0243] The mean difference in S/P of the test lighting from the
reference lighting was 0.14% .+-.0.13% for the 60 lux source, and
0.06%.+-.0.08% for the 150 lux source. The maximum difference was
0.5% and 0.6% respectively.
[0244] One subject was unable to make a match within 70%, and was
further unable to complete all of the brightness matching tests.
This subject was not included in the analysis. Among the remaining
subjects the maximum limen was 20%, while the overall subject mean
limen was 0.7%.+-.1.2% s.e. of the test illuminance. Thus, the BM
study results where the selected reductions amounted to around 20%
can be considered as reliable and not arbitrary resulting from
testing conditions being beyond their discerning capability and we
can be reasonably confident that those differences obtained in the
BM testing are well within the subjects' capabilities.
[0245] Discussion:
[0246] The purpose of the brightness matching was to determine the
adjusted levels of photopic illuminance that would produce
perceptual equality when the S/P values were different. The data
showed that for the 40 subjects with 8 different lighting
conditions, they chose on average to lower the light level of the
higher S/P spectrum for 92% of the trials and depending on the
condition this ranged from 83% to 99%. Thus, we conclude that there
is a trade-off between illuminance and S/P value, i.e. since a
spectrum with a higher S/P value was perceived as brighter in the
comparison study, its photopic illuminance can be lowered by an
amount empirically determined that provides perceptual
equality.
[0247] This result implies that there should be a quantitative
relationship between a given amount of photopic illuminance
difference and an associated difference in S/P value. To evaluate
such a relationship the simple model introduced by Berman et al
(1990) that followed on the classical luminance dependence of
brightness perception was employed. In that model, brightness
perception (B) would depend on luminance (P) as modified by the
multiplicative factor (S/P).sup.n where the exponent n is to be
empirically determined. Since the classical luminance dependence of
brightness perception is provided by a power law the inclusion of
the S/P dependence is assumed to be extended by the equation
LogB=constant.times.[LogP(S/P).sup.n].
[0248] Thus if 2 spectra of different S/P values are perceived as
equally bright at 2 different values of S/P then the above equation
applied at equal values of B can be solved to determine a value for
the exponent n.
[0249] With 8 lighting conditions and 40 subjects there were 320
opportunities to evaluate the exponent n. The analysis led to an
overall exponent value of n=0.436 .+-.0.021 for the entire subject
group covering all 3 age categories. There was no significant
effect of age.
[0250] Correlated Color Temperature (CCT) Variations:
[0251] Prior studies evaluating brightness perception found that
traditionally determined higher color temperature lighting was
perceived as brighter Harrington (1954). But without control of S/P
those comparatively higher CCT spectra associated with
polychromatic light sources will generally have comparatively
higher S/P values. Our premise is that these different brightness
perceptions are a result of different S/P values serving as the
spectral proxy for melanopic content (Berman 2008, Berman &
Clear 2014, Brown 2012) and are not due, per se, to a pure CCT
effect. In the studies performed here we attempted to examine
whether there was a pure traditional (based on CIE chromaticity)
CCT effect on brightness perception and in the selection of
conditions traditional CCT was varied between nominal high around
6500K to low around 2700K. However, for the formation of the
various metamers, we were not able to find a calculational
procedure that allowed constant S/P value but different traditional
CCT values as modifying CCT was always accompanied by a change in
S/P under the constraint of our metamerism. This occurs because
metamers constructed by employing the standard CIE procedure of
equal chromaticity will have the same traditional CCT values as
such metamers also have the same vector distance to the black body
locus. However, as described above, the psychophysically improved
metamers employed here do not have equal CIE chromaticities (see
FIG. 10F) but alternatively they would have equal equivalent
chromaticities in a color space based on the Stockman/Sharpe cone
sensitivities. Nevertheless, in the brightness matching study where
the explicit dependence of brightness perception on S/P via its
exponent could be determined, it was possible to test whether the
exponent had different values depending on the condition of high or
low traditional CCT. This evaluation yielded a difference in the
exponent of 0.013.+-.0.034, which is indistinguishable from zero
and therefore we conclude that there is an absence of any
significant traditional CCT effect on brightness perception.
[0252] Is the Protocol of Rapid Alternation Between Metamers
Accounting for the Full Effect of Melanopsin Activation?
[0253] The results determined here are consistent with present
understanding of melanopsin response from the point of view of an
operative additional spectral sensitivity with a peak response in
the bluish spectral region. The similarity of the results at three
eye illuminances namely 60,150 and 400 Lux in the BC study lend
support that the underlying mechanism is unlikely to be a direct
response of rod receptors. On the other hand, from the
psychophysical approach employed here it is not possible to
conclude whether the spectral effects are a result of a subset of
rapid response melanopsin cells that are directly involved in this
rapidly evaluated brightness perception. Since present
understanding of melanopsin temporal behavior implies a slow
response (McDougal & Gamlin (2010), Bailes& Lucas (2010),
Do&Yau (2010), Ecker (2010) with time periods much longer than
the few seconds employed in the switching protocol it is also
possible that the full tonic response to brightness perception is
not fully established here. Further studies would be useful to
fully elucidate this concern. Perhaps a study performed in a steady
state mode utilizing dichoptic viewing with visual field spectral
optics adjusted to stimulate and allow comparison of
non-overlapping cortical regions associated with each eye might
provide further insight.
[0254] Implications for Lighting Practice:
[0255] In terms of practical applications for lighting engineering,
the results of the BM study show that substantial energy savings
can be achieved by replacing typical HID sources with their
relatively low S/P values with e.g. LED sources capable of much
higher S/P values while maintaining the same brightness perception
even in a nighttime environment where only a fraction of the visual
field is lighted. For example, replacement in a lighted athletic
field employing a typical MH source of S/P=1.4 by a LED source of
S/P=2.4 would lead to the possibility of a 25% light level
reduction (as measured with a standard light meter) based on the
principle of equal perceived brightness and the exponent value of
0.436. This feature is of sufficient magnitude that it should be a
design consideration for sports lighting applications.
REFERENCES:
[0256] Bailes H J, Lucas R J. (2010). Melanopsin and inner retinal
photoreception. Cellular and Molecular Life Sciences, 67(1),
99-111. [0257] Berman S M, Jewett D L, Fein G, Saika G, Ashford F.
(1990), Photopic luminance does not always predict perceived room
brightness. Lighting Research and Technology 1990; 22: 37-41.
[0258] Berman, S. M; 2008, A new retinal photoreceptor should
affect lighting practice Lighting Research and Technology; 40; 373.
[0259] Berman, S M & Clear, R D (2014) Implications of the
Relationship between S/P and Melanopic Efficiency: Illum Eng. Soc
Conference report Nov. 2014. [0260] Brown T M, et al. (2012)
Melanopsin-based brightness discrimination in mice and humans.
CurrBiol 22(12):1134-1141. [0261] CIE (2006) Fundamental
chromaticity diagram with physiological axes--Part 1 Technical
Report 170-1. [0262] Cohen, J B and Kapp auf, W E, (1982) Metameric
color stimuli, fundamental metamers, and Wyszecki's metameric
blacks. The American Journal of Psychology 95(4):537-64. [0263]
Cohen, J B and K app au f, W E (1985), "Color mixture and
fundamental metamers: Theory, algebra, geometry, application",
American Journal of Psychology. 1985 Vol. 98, No 2, pp. 171-259.
[0264] Do M T, Yau K W (2010) Intrinsically photosensitive retinal
ganglion cells. Physiol Rev 90(4):1547-1581. [0265] Ecker J L, et
al. (2010) Melanopsin-expressing retinal ganglion-cell
photoreceptors: Cellular diversity and role in pattern vision.
Neuron 67(1):49-60. [0266] Harrington, R. E. (1954). Effect of
color temperature on apparent brightness. J. Opt. Soc [0267] Lucas
R J, Peirson S N, Berson D M, Brown T M, Cooper H M, Czeisler C A,
Figueiro M G, Gamlin P D, Lockley S W, O'Hagan J B, Price LLA,
Provencio I, Skene D J, Brainard G C (2014) Measuring and using
light in the melanopsin age. Trends in Neurosciences 37:1-9. [0268]
McDougal, D. H. & Gamlin, P. D. 2010 The influence of
intrinsically-photosensitive retinal ganglion cells on the spectral
sensitivity and response dynamics of the human pupillary light
reflex. Vision Res. 50, 72-87. [0269] Royer M P & Houser K W,
(2012) Spatial Brightness Perception of Trichromatic Stimuli:
LeukosVol 9, No2, (Oct)pp.8 9-1 0 8 [0270] Schlesselman et al
(2015), Brightness judgments in a simulated sports field correlate
with the S/P value of light sources. Submitted for presentation IES
Conference Indianapolis, Ind. [0271] Stockman, A., & Sharpe, L.
T. (1999). Cone spectral sensitivities and color matching. In K.
Gegenfurtner& L. T. Sharpe (Eds.), Color vision: From Genes to
Perception (pp. 53-87) Cambridge: Cambridge University Press [0272]
Stockman, A. and Sharpe, L. T. (2000) Spectral sensitivities of the
middle-and long-wavelength sensitive cones derived from
measurements in observers of known genotype. Vision Research, 40,
1711-1737. [0273] Stockman, A., & Sharpe, L. T. (2006).
Physiologically-based colour matching functions. In Proceedings of
the ISCC/CIE Expert Symposium `06: 75 Years of the CIE Standard
Colorimetric Observer (pp. 13-20). Vienna: CIE Central Bureau.
[0274] Vienot, F et al., (2012) "Domain of metamers exciting
intrinsically photosensitive retinal ganglion cells (ipRGCs) and
rods", Journal of Optical Society of America A, Feb. 2012, Vol 29,
No 2, pp. A366-A376.
* * * * *
References